diff --git a/flow-libs/posthtml.js.flow b/flow-libs/posthtml.js.flow
index 32ed17c10bf..1b2131653e9 100644
--- a/flow-libs/posthtml.js.flow
+++ b/flow-libs/posthtml.js.flow
@@ -11,6 +11,11 @@ declare module 'posthtml' {
     tag: string,
     attrs?: {[string]: string, ...},
     content?: Array<string>,
+    loc?: {
+      start: {|line: number, column: number|},
+      end: {|line: number, column: number|},
+      ...
+    },
     ...
   };
 
@@ -26,7 +31,7 @@ declare module 'posthtml' {
     ...
   };
 
-  declare var walk: (fn: (node: PostHTMLNode) => PostHTMLNode) => void;
+  declare var walk: (fn: (node: PostHTMLNode) => PostHTMLNode | PostHTMLNode[]) => void;
   declare var process: (
     tree: PostHTMLTree | string,
     options: ?PostHTMLOptions,
diff --git a/packages/configs/default/index.json b/packages/configs/default/index.json
index 4524fa2ba25..2daad6a34e5 100644
--- a/packages/configs/default/index.json
+++ b/packages/configs/default/index.json
@@ -37,18 +37,11 @@
     "url:*": ["@parcel/transformer-raw"]
   },
   "namers": ["@parcel/namer-default"],
-  "runtimes": {
-    "browser": [
-      "@parcel/runtime-js",
-      "@parcel/runtime-browser-hmr",
-      "@parcel/runtime-react-refresh"
-    ],
-    "service-worker": ["@parcel/runtime-js"],
-    "web-worker": ["@parcel/runtime-js"],
-    "node": ["@parcel/runtime-js"],
-    "electron-renderer": ["@parcel/runtime-js"],
-    "electron-main": ["@parcel/runtime-js"]
-  },
+  "runtimes": [
+    "@parcel/runtime-js",
+    "@parcel/runtime-browser-hmr",
+    "@parcel/runtime-react-refresh"
+  ],
   "optimizers": {
     "data-url:*": ["...", "@parcel/optimizer-data-url"],
     "*.css": ["@parcel/optimizer-cssnano"],
diff --git a/packages/core/core/src/AssetGraph.js b/packages/core/core/src/AssetGraph.js
index 941f94f7376..a107e7d0e0b 100644
--- a/packages/core/core/src/AssetGraph.js
+++ b/packages/core/core/src/AssetGraph.js
@@ -21,6 +21,7 @@ import {md5FromObject} from '@parcel/utils';
 import nullthrows from 'nullthrows';
 import Graph, {type GraphOpts} from './Graph';
 import {createDependency} from './Dependency';
+import {getAssetGroupId} from './assetUtils';
 
 type AssetGraphOpts = {|
   ...GraphOpts<AssetGraphNode>,
@@ -55,13 +56,7 @@ export function nodeFromDep(dep: Dependency): DependencyNode {
 
 export function nodeFromAssetGroup(assetGroup: AssetGroup): AssetGroupNode {
   return {
-    id: md5FromObject({
-      ...assetGroup,
-      // only influences building the asset graph
-      canDefer: undefined,
-      // if only the isURL property is different, no need to re-run transformation.
-      isURL: undefined,
-    }),
+    id: getAssetGroupId(assetGroup),
     type: 'asset_group',
     value: assetGroup,
     usedSymbolsDownDirty: true,
diff --git a/packages/core/core/src/BundleGraph.js b/packages/core/core/src/BundleGraph.js
index 65f93e3a3af..e29827d58da 100644
--- a/packages/core/core/src/BundleGraph.js
+++ b/packages/core/core/src/BundleGraph.js
@@ -23,7 +23,12 @@ import assert from 'assert';
 import invariant from 'assert';
 import crypto from 'crypto';
 import nullthrows from 'nullthrows';
-import {flatMap, objectSortedEntriesDeep, unique} from '@parcel/utils';
+import {
+  flatMap,
+  objectSortedEntriesDeep,
+  unique,
+  isSubset,
+} from '@parcel/utils';
 
 import {getBundleGroupId, getPublicId} from './utils';
 import Graph, {ALL_EDGE_TYPES, mapVisitor, type GraphOpts} from './Graph';
@@ -615,7 +620,7 @@ export default class BundleGraph {
       visitedBundles.add(descendant);
       if (
         descendant.type !== bundle.type ||
-        descendant.env.context !== bundle.env.context
+        !isSubset(descendant.env.context, bundle.env.context)
       ) {
         actions.skipChildren();
         return;
@@ -630,7 +635,7 @@ export default class BundleGraph {
       let similarSiblings = this.getSiblingBundles(descendant).filter(
         sibling =>
           sibling.type === bundle.type &&
-          sibling.env.context === bundle.env.context,
+          isSubset(sibling.env.context, bundle.env.context),
       );
       if (
         similarSiblings.some(
@@ -713,7 +718,7 @@ export default class BundleGraph {
             // Don't deduplicate when context changes
             if (
               node.type === 'bundle' &&
-              node.value.env.context !== bundle.env.context
+              !isSubset(node.value.env.context, bundle.env.context)
             ) {
               actions.skipChildren();
             }
@@ -766,7 +771,7 @@ export default class BundleGraph {
             // Stop when context changes
             if (
               node.type === 'bundle' &&
-              node.value.env.context !== bundle.env.context
+              !isSubset(node.value.env.context, bundle.env.context)
             ) {
               actions.skipChildren();
             }
diff --git a/packages/core/core/src/Environment.js b/packages/core/core/src/Environment.js
index 78a8316a579..30bef706695 100644
--- a/packages/core/core/src/Environment.js
+++ b/packages/core/core/src/Environment.js
@@ -17,6 +17,7 @@ export function createEnvironment({
   isLibrary = false,
   scopeHoist = false,
   sourceMap,
+  loc,
 }: EnvironmentOpts = {}): Environment {
   if (context == null) {
     if (engines?.node) {
@@ -28,58 +29,63 @@ export function createEnvironment({
     }
   }
 
+  let ctx = new Set(typeof context === 'string' ? [context] : context);
+
   if (engines == null) {
-    switch (context) {
-      case 'node':
-      case 'electron-main':
-        engines = {
-          node: DEFAULT_ENGINES.node,
-        };
-        break;
-      case 'browser':
-      case 'web-worker':
-      case 'service-worker':
-      case 'electron-renderer':
-        engines = {
-          browsers: DEFAULT_ENGINES.browsers,
-        };
-        break;
-      default:
-        engines = {};
+    engines = {};
+    for (let context of ctx) {
+      switch (context) {
+        case 'node':
+        case 'electron-main':
+          engines.node = DEFAULT_ENGINES.node;
+          break;
+        case 'browser':
+        case 'web-worker':
+        case 'service-worker':
+        case 'electron-renderer':
+          engines.browsers = DEFAULT_ENGINES.browsers;
+          break;
+      }
     }
   }
 
   if (includeNodeModules == null) {
-    switch (context) {
-      case 'node':
-      case 'electron-main':
-      case 'electron-renderer':
-        includeNodeModules = false;
-        break;
-      case 'browser':
-      case 'web-worker':
-      case 'service-worker':
-      default:
-        includeNodeModules = true;
-        break;
+    includeNodeModules = true;
+    for (let context of ctx) {
+      switch (context) {
+        case 'node':
+        case 'electron-main':
+        case 'electron-renderer':
+          includeNodeModules = false;
+          break;
+        case 'browser':
+        case 'web-worker':
+        case 'service-worker':
+        default:
+          includeNodeModules = true;
+          break;
+      }
     }
   }
 
   if (outputFormat == null) {
-    switch (context) {
-      case 'node':
-      case 'electron-main':
-      case 'electron-renderer':
-        outputFormat = 'commonjs';
-        break;
-      default:
-        outputFormat = 'global';
-        break;
+    outputFormat = 'global';
+    for (let context of ctx) {
+      switch (context) {
+        case 'node':
+        case 'electron-main':
+        case 'electron-renderer':
+          outputFormat = 'commonjs';
+          break;
+        default:
+          outputFormat = 'global';
+          break;
+      }
     }
   }
 
   return {
-    context,
+    context: ctx,
     engines,
     includeNodeModules,
     outputFormat,
@@ -87,6 +93,7 @@ export function createEnvironment({
     minify,
     scopeHoist,
     sourceMap,
+    loc,
   };
 }
 
diff --git a/packages/core/core/src/PackagerRunner.js b/packages/core/core/src/PackagerRunner.js
index eae47bf4b9e..d02d53a03bf 100644
--- a/packages/core/core/src/PackagerRunner.js
+++ b/packages/core/core/src/PackagerRunner.js
@@ -421,7 +421,7 @@ export default class PackagerRunner {
         sourceRoot = bundle.env.sourceMap.sourceRoot;
       } else if (
         this.options.serve &&
-        bundle.target.env.context === 'browser'
+        bundle.target.env.context.has('browser')
       ) {
         sourceRoot = '/__parcel_source_root';
       }
@@ -431,7 +431,7 @@ export default class PackagerRunner {
         bundle.env.sourceMap.inlineSources !== undefined
       ) {
         inlineSources = bundle.env.sourceMap.inlineSources;
-      } else if (bundle.target.env.context !== 'node') {
+      } else if (!bundle.target.env.context.has('node')) {
         // inlining should only happen in production for browser targets by default
         inlineSources = this.options.mode === 'production';
       }
diff --git a/packages/core/core/src/ParcelConfig.js b/packages/core/core/src/ParcelConfig.js
index 400785cc5bc..ddb6524368d 100644
--- a/packages/core/core/src/ParcelConfig.js
+++ b/packages/core/core/src/ParcelConfig.js
@@ -7,7 +7,6 @@ import type {
   Bundler,
   Namer,
   Runtime,
-  EnvironmentContext,
   PackageName,
   Optimizer,
   Packager,
@@ -52,7 +51,7 @@ export default class ParcelConfig {
   transformers: GlobMap<ExtendableParcelConfigPipeline>;
   bundler: ?ParcelPluginNode;
   namers: PureParcelConfigPipeline;
-  runtimes: {[EnvironmentContext]: PureParcelConfigPipeline, ...};
+  runtimes: PureParcelConfigPipeline;
   packagers: GlobMap<ParcelPluginNode>;
   validators: GlobMap<ExtendableParcelConfigPipeline>;
   optimizers: GlobMap<ExtendableParcelConfigPipeline>;
@@ -71,7 +70,7 @@ export default class ParcelConfig {
     this.filePath = config.filePath;
     this.resolvers = config.resolvers || [];
     this.transformers = config.transformers || {};
-    this.runtimes = config.runtimes || {};
+    this.runtimes = config.runtimes || [];
     this.bundler = config.bundler;
     this.namers = config.namers || [];
     this.packagers = config.packagers || {};
@@ -266,10 +265,8 @@ export default class ParcelConfig {
     return this.loadPlugins<Namer>(this.namers);
   }
 
-  getRuntimes(
-    context: EnvironmentContext,
-  ): Promise<Array<LoadedPlugin<Runtime>>> {
-    let runtimes = this.runtimes[context];
+  getRuntimes(): Promise<Array<LoadedPlugin<Runtime>>> {
+    let runtimes = this.runtimes;
     if (!runtimes) {
       return Promise.resolve([]);
     }
diff --git a/packages/core/core/src/ParcelConfig.schema.js b/packages/core/core/src/ParcelConfig.schema.js
index e0076de6a27..a54152577a2 100644
--- a/packages/core/core/src/ParcelConfig.schema.js
+++ b/packages/core/core/src/ParcelConfig.schema.js
@@ -122,7 +122,7 @@ export default {
     packagers: (mapStringSchema('packager', 'packagers'): SchemaEntity),
     optimizers: (mapPipelineSchema('optimizer', 'optimizers'): SchemaEntity),
     reporters: (pipelineSchema('reporter', 'reporters'): SchemaEntity),
-    runtimes: (mapPipelineSchema('runtime', 'runtimes'): SchemaEntity),
+    runtimes: (pipelineSchema('runtime', 'runtimes'): SchemaEntity),
     filePath: {
       type: 'string',
     },
diff --git a/packages/core/core/src/Transformation.js b/packages/core/core/src/Transformation.js
index fdf493d9e93..b72b8061e70 100644
--- a/packages/core/core/src/Transformation.js
+++ b/packages/core/core/src/Transformation.js
@@ -402,7 +402,17 @@ export default class Transformation {
           .filter(
             asset =>
               asset.ast != null &&
-              !(asset.value.type === 'js' && asset.value.env.scopeHoist),
+              !(
+                asset.value.type === 'js' &&
+                asset.value.env.scopeHoist &&
+                // HACK: also handle global scripts with no dependencies.
+                // JSPackager calls getCode() for these even with scope hoisting, so we
+                // need to generate here until we find a way to make generate happen on demand.
+                !(
+                  asset.value.env.context.has('script') &&
+                  asset.value.dependencies.size === 0
+                )
+              ),
           )
           .map(async asset => {
             if (asset.isASTDirty) {
diff --git a/packages/core/core/src/applyRuntimes.js b/packages/core/core/src/applyRuntimes.js
index 593e739d771..10e25b8e3c8 100644
--- a/packages/core/core/src/applyRuntimes.js
+++ b/packages/core/core/src/applyRuntimes.js
@@ -22,6 +22,7 @@ import {setDifference} from '@parcel/utils';
 import {PluginLogger} from '@parcel/logger';
 import ThrowableDiagnostic, {errorToDiagnostic} from '@parcel/diagnostic';
 import {dependencyToInternalDependency} from './public/Dependency';
+import {mergeEnvironments} from './Environment';
 
 type RuntimeConnection = {|
   bundle: InternalBundle,
@@ -46,7 +47,7 @@ export default async function applyRuntimes({
   let connections: Array<RuntimeConnection> = [];
 
   for (let bundle of bundleGraph.getBundles()) {
-    let runtimes = await config.getRuntimes(bundle.env.context);
+    let runtimes = await config.getRuntimes();
     for (let runtime of runtimes) {
       try {
         let applied = await runtime.plugin.apply({
@@ -62,11 +63,17 @@ export default async function applyRuntimes({
 
         if (applied) {
           let runtimeAssets = Array.isArray(applied) ? applied : [applied];
-          for (let {code, dependency, filePath, isEntry} of runtimeAssets) {
+          for (let {
+            code,
+            dependency,
+            filePath,
+            isEntry,
+            env,
+          } of runtimeAssets) {
             let assetGroup = {
               code,
               filePath,
-              env: bundle.env,
+              env: mergeEnvironments(bundle.env, env),
               // Runtime assets should be considered source, as they should be
               // e.g. compiled to run in the target environment
               isSource: true,
diff --git a/packages/core/core/src/assetUtils.js b/packages/core/core/src/assetUtils.js
index fd6e45ed935..f332eb019ff 100644
--- a/packages/core/core/src/assetUtils.js
+++ b/packages/core/core/src/assetUtils.js
@@ -14,6 +14,7 @@ import type {
 } from '@parcel/types';
 import type {
   Asset,
+  AssetGroup,
   RequestInvalidation,
   Dependency,
   Environment,
@@ -24,6 +25,7 @@ import type {ConfigOutput} from '@parcel/utils';
 import {Readable} from 'stream';
 import crypto from 'crypto';
 import {PluginLogger} from '@parcel/logger';
+import {md5FromObject} from '@parcel/utils';
 import nullthrows from 'nullthrows';
 import CommittedAsset from './CommittedAsset';
 import UncommittedAsset from './UncommittedAsset';
@@ -251,3 +253,14 @@ export async function getInvalidationHash(
 
   return hash.digest('hex');
 }
+
+export function getAssetGroupId(assetGroup: AssetGroup): string {
+  return md5FromObject({
+    ...assetGroup,
+    env: getEnvironmentHash(assetGroup.env),
+    // only influences building the asset graph
+    canDefer: undefined,
+    // if only the isURL property is different, no need to re-run transformation.
+    isURL: undefined,
+  });
+}
diff --git a/packages/core/core/src/dumpGraphToGraphViz.js b/packages/core/core/src/dumpGraphToGraphViz.js
index f98f0dbf979..6f7799835cb 100644
--- a/packages/core/core/src/dumpGraphToGraphViz.js
+++ b/packages/core/core/src/dumpGraphToGraphViz.js
@@ -138,10 +138,11 @@ export default async function dumpGraphToGraphViz(
 
 function getEnvDescription(env: Environment) {
   let description;
+  let context = [...env.context].join(', ');
   if (typeof env.engines.browsers === 'string') {
-    description = `${env.context}: ${env.engines.browsers}`;
+    description = `${context}: ${env.engines.browsers}`;
   } else if (Array.isArray(env.engines.browsers)) {
-    description = `${env.context}: ${env.engines.browsers.join(', ')}`;
+    description = `${context}: ${env.engines.browsers.join(', ')}`;
   } else if (env.engines.node) {
     description = `node: ${env.engines.node}`;
   } else if (env.engines.electron) {
diff --git a/packages/core/core/src/public/Environment.js b/packages/core/core/src/public/Environment.js
index 9f1283b93e2..d1bcd892471 100644
--- a/packages/core/core/src/public/Environment.js
+++ b/packages/core/core/src/public/Environment.js
@@ -2,26 +2,35 @@
 import type {
   Environment as IEnvironment,
   EnvironmentContext,
+  EnvironmentFeature,
   Engines,
   OutputFormat,
   PackageName,
   VersionMap,
   TargetSourceMapOptions,
+  SourceLocation,
 } from '@parcel/types';
 import type {Environment as InternalEnvironment} from '../types';
 import nullthrows from 'nullthrows';
 import browserslist from 'browserslist';
 import semver from 'semver';
+import {setIntersects} from '@parcel/utils';
 
-export const BROWSER_ENVS: Set<string> = new Set<string>([
+export const BROWSER_ENVS: Set<EnvironmentContext> = new Set([
   'browser',
   'web-worker',
   'service-worker',
   'electron-renderer',
 ]);
-const ELECTRON_ENVS = new Set(['electron-main', 'electron-renderer']);
-const NODE_ENVS = new Set(['node', ...ELECTRON_ENVS]);
-const WORKER_ENVS = new Set(['web-worker', 'service-worker']);
+const ELECTRON_ENVS = new Set<EnvironmentContext>([
+  'electron-main',
+  'electron-renderer',
+]);
+const NODE_ENVS = new Set<EnvironmentContext>(['node', ...ELECTRON_ENVS]);
+const WORKER_ENVS = new Set<EnvironmentContext>([
+  'web-worker',
+  'service-worker',
+]);
 const ISOLATED_ENVS = WORKER_ENVS;
 
 const ALL_BROWSERS = [
@@ -45,17 +54,39 @@ const ALL_BROWSERS = [
   'kaios',
 ];
 
-const ESMODULE_BROWSERS = {
-  edge: '16',
-  firefox: '60',
-  chrome: '61',
-  safari: '11',
-  opera: '48',
-  ios: '11',
-  android: '76',
-  and_chr: '76',
-  and_ff: '68',
-  samsung: '8.2',
+const supportData = {
+  esmodules: {
+    edge: '16',
+    firefox: '60',
+    chrome: '61',
+    safari: '11',
+    opera: '48',
+    ios: '11',
+    android: '76',
+    and_chr: '76',
+    and_ff: '68',
+    samsung: '8.2',
+  },
+  'dynamic-import': {
+    edge: '76',
+    firefox: '67',
+    chrome: '63',
+    safari: '11.1',
+    opera: '50',
+    ios: '11.3',
+    android: '63',
+    and_chr: '63',
+    and_ff: '67',
+    samsung: '8',
+  },
+  'worker-type': {
+    edge: '80',
+    chrome: '80',
+    opera: '67',
+    android: '81',
+    and_chr: '86',
+  },
+  'service-worker-type': {},
 };
 
 const internalEnvironmentToEnvironment: WeakMap<
@@ -87,7 +118,7 @@ export default class Environment implements IEnvironment {
     return this;
   }
 
-  get context(): EnvironmentContext {
+  get context(): Set<EnvironmentContext> {
     return this.#environment.context;
   }
 
@@ -122,24 +153,28 @@ export default class Environment implements IEnvironment {
     return this.#environment.sourceMap;
   }
 
+  get loc(): ?SourceLocation {
+    return this.#environment.loc;
+  }
+
   isBrowser(): boolean {
-    return BROWSER_ENVS.has(this.#environment.context);
+    return setIntersects(this.#environment.context, BROWSER_ENVS);
   }
 
   isNode(): boolean {
-    return NODE_ENVS.has(this.#environment.context);
+    return setIntersects(this.#environment.context, NODE_ENVS);
   }
 
   isElectron(): boolean {
-    return ELECTRON_ENVS.has(this.#environment.context);
+    return setIntersects(this.#environment.context, ELECTRON_ENVS);
   }
 
   isIsolated(): boolean {
-    return ISOLATED_ENVS.has(this.#environment.context);
+    return setIntersects(this.#environment.context, ISOLATED_ENVS);
   }
 
   isWorker(): boolean {
-    return WORKER_ENVS.has(this.#environment.context);
+    return setIntersects(this.#environment.context, WORKER_ENVS);
   }
 
   matchesEngines(minVersions: VersionMap): boolean {
@@ -155,7 +190,7 @@ export default class Environment implements IEnvironment {
 
       // If outputting esmodules, exclude browsers without support.
       if (this.outputFormat === 'esmodule') {
-        browsers = [...browsers, ...getExcludedBrowsers(ESMODULE_BROWSERS)];
+        browsers = [...browsers, ...getExcludedBrowsers(supportData.esmodules)];
       }
 
       let matchedBrowsers = browserslist(browsers);
@@ -168,6 +203,15 @@ export default class Environment implements IEnvironment {
 
     return false;
   }
+
+  supports(feature: EnvironmentFeature): boolean {
+    let engines = supportData[feature];
+    if (!engines) {
+      throw new Error('Unknown environment feature: ' + feature);
+    }
+
+    return this.matchesEngines(engines);
+  }
 }
 
 function getExcludedBrowsers(minVersions: VersionMap) {
diff --git a/packages/core/core/src/requests/AssetRequest.js b/packages/core/core/src/requests/AssetRequest.js
index 0a06b35928b..2b84a9a0a8c 100644
--- a/packages/core/core/src/requests/AssetRequest.js
+++ b/packages/core/core/src/requests/AssetRequest.js
@@ -9,6 +9,7 @@ import type {TransformationResult} from '../Transformation';
 import {md5FromObject} from '@parcel/utils';
 import nullthrows from 'nullthrows';
 import createParcelConfigRequest from './ParcelConfigRequest';
+import {getAssetGroupId} from '../assetUtils';
 
 type RunInput = {|
   input: AssetRequestInput,
@@ -42,7 +43,7 @@ const type = 'asset_request';
 function getId(input: AssetRequestInput) {
   // eslint-disable-next-line no-unused-vars
   let {optionsRef, ...hashInput} = input;
-  return `${type}:${md5FromObject(hashInput)}`;
+  return `${type}:${getAssetGroupId(hashInput)}`;
 }
 
 async function run({input, api, options, farm}: RunInput) {
diff --git a/packages/core/core/src/requests/ParcelConfigRequest.js b/packages/core/core/src/requests/ParcelConfigRequest.js
index 0f1e5ca120c..d41b6132715 100644
--- a/packages/core/core/src/requests/ParcelConfigRequest.js
+++ b/packages/core/core/src/requests/ParcelConfigRequest.js
@@ -269,7 +269,11 @@ export function processConfig(
           }
         : undefined,
     namers: processPipeline(configFile.namers, '/namers', configFile.filePath),
-    runtimes: processMap(configFile.runtimes, '/runtimes', configFile.filePath),
+    runtimes: processPipeline(
+      configFile.runtimes,
+      '/runtimes',
+      configFile.filePath,
+    ),
     packagers: processMap(
       configFile.packagers,
       '/packagers',
@@ -491,7 +495,7 @@ export function mergeConfigs(
     validators: mergeMaps(base.validators, ext.validators, mergePipelines),
     bundler: ext.bundler || base.bundler,
     namers: mergePipelines(base.namers, ext.namers),
-    runtimes: mergeMaps(base.runtimes, ext.runtimes, mergePipelines),
+    runtimes: mergePipelines(base.runtimes, ext.runtimes),
     packagers: mergeMaps(base.packagers, ext.packagers),
     optimizers: mergeMaps(base.optimizers, ext.optimizers, mergePipelines),
     reporters: mergePipelines(base.reporters, ext.reporters),
diff --git a/packages/core/core/src/requests/TargetRequest.js b/packages/core/core/src/requests/TargetRequest.js
index 8c88cfe044c..cc5cba9e392 100644
--- a/packages/core/core/src/requests/TargetRequest.js
+++ b/packages/core/core/src/requests/TargetRequest.js
@@ -24,6 +24,7 @@ import {
   resolveConfig,
   md5FromObject,
   validateSchema,
+  setIntersects,
 } from '@parcel/utils';
 import {createEnvironment} from '../Environment';
 import createParcelConfigRequest from './ParcelConfigRequest';
@@ -199,7 +200,7 @@ export class TargetResolver {
             },
           });
         }
-        if (!BROWSER_ENVS.has(targets[0].env.context)) {
+        if (!setIntersects(BROWSER_ENVS, targets[0].env.context)) {
           throw new ThrowableDiagnostic({
             diagnostic: {
               message: `Only browser targets are supported in serve mode`,
diff --git a/packages/core/core/src/types.js b/packages/core/core/src/types.js
index 70a819fcaaf..9b0a3e98364 100644
--- a/packages/core/core/src/types.js
+++ b/packages/core/core/src/types.js
@@ -50,7 +50,7 @@ export type ProcessedParcelConfig = {|
   transformers?: {[Glob]: ExtendableParcelConfigPipeline, ...},
   bundler: ?ParcelPluginNode,
   namers?: PureParcelConfigPipeline,
-  runtimes?: {[EnvironmentContext]: PureParcelConfigPipeline, ...},
+  runtimes?: PureParcelConfigPipeline,
   packagers?: {[Glob]: ParcelPluginNode, ...},
   optimizers?: {[Glob]: ExtendableParcelConfigPipeline, ...},
   reporters?: PureParcelConfigPipeline,
@@ -60,7 +60,7 @@ export type ProcessedParcelConfig = {|
 |};
 
 export type Environment = {|
-  context: EnvironmentContext,
+  context: Set<EnvironmentContext>,
   engines: Engines,
   includeNodeModules:
     | boolean
@@ -71,6 +71,7 @@ export type Environment = {|
   minify: boolean,
   scopeHoist: boolean,
   sourceMap: ?TargetSourceMapOptions,
+  loc: ?SourceLocation,
 |};
 
 export type Target = {|
diff --git a/packages/core/core/test/Environment.test.js b/packages/core/core/test/Environment.test.js
index 40dd9b048f9..733097e4bfd 100644
--- a/packages/core/core/test/Environment.test.js
+++ b/packages/core/core/test/Environment.test.js
@@ -6,7 +6,7 @@ import {createEnvironment} from '../src/Environment';
 describe('Environment', () => {
   it('assigns a default environment with nothing passed', () => {
     assert.deepEqual(createEnvironment(), {
-      context: 'browser',
+      context: new Set(['browser']),
       engines: {
         browsers: ['> 0.25%'],
       },
@@ -16,12 +16,13 @@ describe('Environment', () => {
       minify: false,
       scopeHoist: false,
       sourceMap: undefined,
+      loc: undefined,
     });
   });
 
   it('assigns a node context if a node engine is given', () => {
     assert.deepEqual(createEnvironment({engines: {node: '>= 10.0.0'}}), {
-      context: 'node',
+      context: new Set(['node']),
       engines: {
         node: '>= 10.0.0',
       },
@@ -31,6 +32,7 @@ describe('Environment', () => {
       minify: false,
       scopeHoist: false,
       sourceMap: undefined,
+      loc: undefined,
     });
   });
 
@@ -38,7 +40,7 @@ describe('Environment', () => {
     assert.deepEqual(
       createEnvironment({engines: {browsers: ['last 1 version']}}),
       {
-        context: 'browser',
+        context: new Set(['browser']),
         engines: {
           browsers: ['last 1 version'],
         },
@@ -48,13 +50,14 @@ describe('Environment', () => {
         minify: false,
         scopeHoist: false,
         sourceMap: undefined,
+        loc: undefined,
       },
     );
   });
 
   it('assigns default engines for node', () => {
     assert.deepEqual(createEnvironment({context: 'node'}), {
-      context: 'node',
+      context: new Set(['node']),
       engines: {
         node: '>= 8.0.0',
       },
@@ -64,12 +67,13 @@ describe('Environment', () => {
       minify: false,
       scopeHoist: false,
       sourceMap: undefined,
+      loc: undefined,
     });
   });
 
   it('assigns default engines for browsers', () => {
     assert.deepEqual(createEnvironment({context: 'browser'}), {
-      context: 'browser',
+      context: new Set(['browser']),
       engines: {
         browsers: ['> 0.25%'],
       },
@@ -79,6 +83,7 @@ describe('Environment', () => {
       minify: false,
       scopeHoist: false,
       sourceMap: undefined,
+      loc: undefined,
     });
   });
 });
diff --git a/packages/core/core/test/ParcelConfigRequest.test.js b/packages/core/core/test/ParcelConfigRequest.test.js
index 572caf8d19c..509f4d38570 100644
--- a/packages/core/core/test/ParcelConfigRequest.test.js
+++ b/packages/core/core/test/ParcelConfigRequest.test.js
@@ -568,7 +568,7 @@ describe('loadParcelConfig', () => {
           resolveFrom: '.parcelrc',
           keyPath: '/bundler',
         },
-        runtimes: {},
+        runtimes: [],
         namers: [],
         optimizers: {},
         packagers: {},
diff --git a/packages/core/core/test/TargetRequest.test.js b/packages/core/core/test/TargetRequest.test.js
index 643450d51e3..1a74e436d31 100644
--- a/packages/core/core/test/TargetRequest.test.js
+++ b/packages/core/core/test/TargetRequest.test.js
@@ -103,7 +103,7 @@ describe('TargetResolver', () => {
           publicUrl: '/',
           distDir: path.resolve('customA'),
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             includeNodeModules: true,
             engines: {
               browsers: ['> 0.25%'],
@@ -113,6 +113,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
         },
         {
@@ -120,7 +121,7 @@ describe('TargetResolver', () => {
           publicUrl: '/',
           distDir: path.resolve('customB'),
           env: {
-            context: 'node',
+            context: new Set(['node']),
             includeNodeModules: false,
             engines: {
               node: '>= 8.0.0',
@@ -130,6 +131,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
         },
       ],
@@ -148,7 +150,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'node',
+            context: new Set(['node']),
             engines: {
               node: '>= 8.0.0',
             },
@@ -158,6 +160,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(COMMON_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -177,7 +180,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['last 1 version'],
             },
@@ -189,6 +192,7 @@ describe('TargetResolver', () => {
             sourceMap: {
               inlineSources: true,
             },
+            loc: undefined,
           },
           loc: {
             filePath: path.join(COMMON_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -208,7 +212,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/assets',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['last 1 version'],
             },
@@ -218,6 +222,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(COMMON_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -247,7 +252,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'node',
+            context: new Set(['node']),
             engines: {
               node: '>= 8.0.0',
             },
@@ -257,6 +262,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: undefined,
+            loc: undefined,
           },
           loc: {
             filePath: path.join(
@@ -288,7 +294,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'node',
+            context: new Set(['node']),
             engines: {
               node: '>= 8.0.0',
             },
@@ -298,6 +304,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(CUSTOM_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -320,7 +327,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['last 1 version'],
             },
@@ -330,6 +337,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(CUSTOM_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -352,7 +360,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['ie11'],
             },
@@ -362,6 +370,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(CUSTOM_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -390,7 +399,7 @@ describe('TargetResolver', () => {
           distEntry: undefined,
           publicUrl: 'www',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: '> 0.25%',
             },
@@ -400,6 +409,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: undefined,
         },
@@ -416,7 +426,7 @@ describe('TargetResolver', () => {
         distEntry: 'index.js',
         publicUrl: '/',
         env: {
-          context: 'node',
+          context: new Set(['node']),
           engines: {},
           includeNodeModules: false,
           isLibrary: true,
@@ -424,6 +434,7 @@ describe('TargetResolver', () => {
           minify: false,
           scopeHoist: false,
           sourceMap: {},
+          loc: undefined,
         },
         loc: {
           filePath: path.join(CONTEXT_FIXTURE_PATH, 'package.json'),
@@ -450,7 +461,7 @@ describe('TargetResolver', () => {
         distEntry: 'index.html',
         publicUrl: '/',
         env: {
-          context: 'browser',
+          context: new Set(['browser']),
           engines: {},
           includeNodeModules: true,
           isLibrary: false,
@@ -458,6 +469,7 @@ describe('TargetResolver', () => {
           minify: false,
           scopeHoist: false,
           sourceMap: {},
+          loc: undefined,
         },
         loc: {
           filePath: path.join(fixture, 'package.json'),
@@ -489,7 +501,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/',
           env: {
-            context: 'node',
+            context: new Set(['node']),
             engines: {
               node: '>= 8.0.0',
             },
@@ -499,6 +511,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(COMMON_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -518,7 +531,7 @@ describe('TargetResolver', () => {
           distEntry: 'index.js',
           publicUrl: '/assets',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['last 1 version'],
             },
@@ -528,6 +541,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: {
             filePath: path.join(COMMON_TARGETS_FIXTURE_PATH, 'package.json'),
@@ -561,7 +575,7 @@ describe('TargetResolver', () => {
           distDir: serveDistDir,
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {},
             includeNodeModules: true,
             outputFormat: 'global',
@@ -569,6 +583,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
         },
       ],
@@ -586,7 +601,7 @@ describe('TargetResolver', () => {
           distDir: path.join(DEFAULT_DISTPATH_FIXTURE_PATHS.none, 'dist'),
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['Chrome 80'],
             },
@@ -596,6 +611,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
         },
       ],
@@ -614,7 +630,7 @@ describe('TargetResolver', () => {
           distEntry: undefined,
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['Chrome 80'],
             },
@@ -624,6 +640,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: undefined,
         },
@@ -647,7 +664,7 @@ describe('TargetResolver', () => {
           distEntry: undefined,
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['last 1 version'],
             },
@@ -657,6 +674,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: undefined,
         },
@@ -670,7 +688,7 @@ describe('TargetResolver', () => {
           distEntry: undefined,
           publicUrl: '/',
           env: {
-            context: 'browser',
+            context: new Set(['browser']),
             engines: {
               browsers: ['IE 11'],
             },
@@ -680,6 +698,7 @@ describe('TargetResolver', () => {
             minify: false,
             scopeHoist: false,
             sourceMap: {},
+            loc: undefined,
           },
           loc: undefined,
         },
diff --git a/packages/core/integration-tests/test/cache.js b/packages/core/integration-tests/test/cache.js
index 4e1de620e17..8682d31b1fe 100644
--- a/packages/core/integration-tests/test/cache.js
+++ b/packages/core/integration-tests/test/cache.js
@@ -1808,7 +1808,7 @@ describe('cache', function() {
             'utf8',
           );
           assert(
-            contents.includes('<script src="http://example.com'),
+            contents.includes('<script type="module" src="http://example.com'),
             'should include example.com',
           );
 
@@ -1832,7 +1832,9 @@ describe('cache', function() {
         'utf8',
       );
       assert(
-        contents.includes('<script src="http://mygreatwebsite.com'),
+        contents.includes(
+          '<script type="module" src="http://mygreatwebsite.com',
+        ),
         'should include example.com',
       );
     });
@@ -2146,7 +2148,7 @@ describe('cache', function() {
             'utf8',
           );
           assert(
-            contents.includes('<script src="http://example.com'),
+            contents.includes('<script type="module" src="http://example.com'),
             'should include example.com',
           );
 
@@ -2161,7 +2163,9 @@ describe('cache', function() {
         'utf8',
       );
       assert(
-        contents.includes('<script src="http://mygreatwebsite.com'),
+        contents.includes(
+          '<script type="module" src="http://mygreatwebsite.com',
+        ),
         'should include example.com',
       );
     });
diff --git a/packages/core/integration-tests/test/html.js b/packages/core/integration-tests/test/html.js
index 2c4ff69d0c0..b5578d1f4d0 100644
--- a/packages/core/integration-tests/test/html.js
+++ b/packages/core/integration-tests/test/html.js
@@ -956,7 +956,150 @@ describe('html', function() {
     assert(!html.includes('@import'));
   });
 
-  it('should allow imports and requires in inline <script> tags', async function() {
+  it('should expose top level declarations globally in inline <script> tags', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/html-inline-js-script/globals.html'),
+    );
+
+    let logs = [];
+    let ctx = await run(
+      b,
+      {
+        log(bar, baz) {
+          logs.push([bar, baz]);
+        },
+      },
+      {require: false},
+    );
+    let output = ctx.output;
+    assert.equal(output.x, 2);
+    assert.equal(output.y, 'undefined');
+    assert.equal(output.z, 4);
+    assert.equal(typeof output.bar, 'function');
+    assert.equal(output.Test, 'undefined');
+    assert.equal(typeof output.Foo, 'function');
+    assert.equal(typeof output.baz, 'function');
+
+    // x is a let, so is "global" but not part of the global object
+    assert(!('x' in ctx));
+    assert(!('y' in ctx));
+    assert.equal(ctx.z, 4);
+    assert.equal(typeof ctx.bar, 'function');
+    assert(!('Test' in ctx));
+    assert(!('Foo' in ctx));
+    assert.equal(typeof ctx.baz, 'function');
+
+    assert.deepEqual(logs, [
+      ['undefined', 'function'],
+      ['function', 'function'],
+      ['function', 'function'],
+    ]);
+  });
+
+  for (let scopeHoist of [false, true]) {
+    it(
+      'should expose top level declarations globally in inline <script> tags with dependencies with scopeHoist = ' +
+        scopeHoist,
+      async function() {
+        let b = await bundle(
+          path.join(
+            __dirname,
+            '/integration/html-inline-js-script/globals-dependencies.html',
+          ),
+          {scopeHoist},
+        );
+
+        let logs = [];
+        let ctx = await run(
+          b,
+          {
+            log(bar, baz) {
+              logs.push([bar, baz]);
+            },
+          },
+          {require: false},
+        );
+        let output = ctx.output;
+        assert.equal(output.x, 2);
+        assert.equal(output.y, 'undefined');
+        assert.equal(output.z, 4);
+        assert.equal(typeof output.bar, 'function');
+        assert.equal(output.Test, 'undefined');
+        assert.equal(typeof output.Foo, 'function');
+        assert.equal(typeof output.baz, 'function');
+
+        // x is a let, so is "global" but not part of the global object
+        assert(!('x' in ctx));
+        assert(!('y' in ctx));
+        assert.equal(ctx.z, 4);
+        assert.equal(typeof ctx.bar, 'function');
+        assert(!('Test' in ctx));
+        assert(!('Foo' in ctx));
+        assert.equal(typeof ctx.baz, 'function');
+
+        assert.deepEqual(logs, [
+          ['undefined', 'function'],
+          ['function', 'function'],
+          ['function', 'function'],
+        ]);
+
+        let contents = await outputFS.readFile(
+          b.getBundles()[0].filePath,
+          'utf8',
+        );
+        if (scopeHoist) {
+          assert(contents.includes('import('));
+        } else {
+          assert(!contents.includes('import('));
+        }
+      },
+    );
+  }
+
+  it('should error on imports in inline scripts without type="module"', async function() {
+    let errored = false;
+    try {
+      await bundle(
+        path.join(__dirname, '/integration/html-inline-js-script/error.html'),
+      );
+    } catch (err) {
+      assert.equal(
+        err.message,
+        'Browser scripts cannot have imports or exports. Use a <script type="module"> instead.',
+      );
+      assert.deepEqual(err.diagnostics, [
+        {
+          message:
+            'Browser scripts cannot have imports or exports. Use a <script type="module"> instead.',
+          filePath: path.join(
+            __dirname,
+            '/integration/html-inline-js-script/error.html',
+          ),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 5,
+                  column: 7,
+                },
+                end: {
+                  line: 5,
+                  column: 24,
+                },
+              },
+            ],
+          },
+        },
+      ]);
+
+      errored = true;
+    }
+
+    assert(errored);
+  });
+
+  it('should allow imports and requires in inline <script type="module"> tags', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/html-inline-js-require/index.html'),
       {minify: true},
@@ -1027,13 +1170,192 @@ describe('html', function() {
     assert(html.includes('document.write("Hello world")'));
   });
 
+  it('should compile inline <script type="module"> to non-module if not all engines support esmodules', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/html-inline-js-module/index.html'),
+      {
+        production: true,
+        scopeHoist: true,
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
+    );
+
+    await assertBundles(b, [
+      {
+        type: 'js',
+        assets: ['index.html'],
+      },
+      {
+        name: 'index.html',
+        assets: ['index.html'],
+      },
+    ]);
+
+    let html = await outputFS.readFile(
+      path.join(distDir, 'index.html'),
+      'utf8',
+    );
+    assert(!html.includes('<script type="module">'));
+    assert(html.includes('<script>'));
+    assert(html.includes('document.write("Hello world")'));
+  });
+
+  it('should compile a module and nomodule script when not all engines support esmodules natively', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/html-js/index.html'),
+      {
+        production: true,
+        scopeHoist: true,
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
+    );
+
+    await assertBundles(b, [
+      {
+        type: 'js',
+        assets: ['index.js', 'other.js'],
+      },
+      {
+        type: 'js',
+        assets: ['index.js', 'other.js'],
+      },
+      {
+        name: 'index.html',
+        assets: ['index.html'],
+      },
+    ]);
+
+    let html = await outputFS.readFile(
+      path.join(distDir, 'index.html'),
+      'utf8',
+    );
+    assert(html.includes('<script type="module" src='));
+    assert(/<script src=".*?" nomodule/.test(html));
+  });
+
+  it('should remove type="module" when not scope hoisting', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/html-js/index.html'),
+    );
+
+    await assertBundles(b, [
+      {
+        type: 'js',
+        assets: ['index.js', 'other.js'],
+      },
+      {
+        name: 'index.html',
+        assets: ['index.html'],
+      },
+    ]);
+
+    let html = await outputFS.readFile(
+      path.join(distDir, 'index.html'),
+      'utf8',
+    );
+    assert(!html.includes('<script type="module"'));
+    assert(html.includes('<script src='));
+  });
+
+  it('should not add a nomodule version when all browsers support esmodules', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/html-js/index.html'),
+      {scopeHoist: true},
+    );
+
+    await assertBundles(b, [
+      {
+        type: 'js',
+        assets: ['index.js', 'other.js'],
+      },
+      {
+        name: 'index.html',
+        assets: ['index.html'],
+      },
+    ]);
+
+    let html = await outputFS.readFile(
+      path.join(distDir, 'index.html'),
+      'utf8',
+    );
+    assert(html.includes('<script type="module" src='));
+    assert(!/<script src=".*?" nomodule/.test(html));
+  });
+
+  it('should error on imports in scripts without type="module"', async function() {
+    let errored = false;
+    try {
+      await bundle(path.join(__dirname, '/integration/html-js/error.html'));
+    } catch (err) {
+      assert.equal(
+        err.message,
+        'Browser scripts cannot have imports or exports. Use a <script type="module"> instead.',
+      );
+      assert.deepEqual(err.diagnostics, [
+        {
+          message:
+            'Browser scripts cannot have imports or exports. Use a <script type="module"> instead.',
+          filePath: path.join(__dirname, '/integration/html-js/index.js'),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 1,
+                  column: 1,
+                },
+                end: {
+                  line: 1,
+                  column: 29,
+                },
+              },
+            ],
+          },
+        },
+        {
+          message: 'The environment was originally created here:',
+          filePath: path.join(__dirname, '/integration/html-js/error.html'),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 1,
+                  column: 1,
+                },
+                end: {
+                  line: 1,
+                  column: 32,
+                },
+              },
+            ],
+          },
+        },
+      ]);
+
+      errored = true;
+    }
+
+    assert(errored);
+  });
+
   it('should correctly bundle loaders for nested dynamic imports', async function() {
     let b = await bundle(
       path.join(
         __dirname,
         '/integration/html-js-shared-dynamic-nested/index.html',
       ),
-      {production: true, scopeHoist: true},
+      {
+        production: true,
+        scopeHoist: true,
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
     );
 
     await assertBundles(b, [
@@ -1053,6 +1375,19 @@ describe('html', function() {
           'relative-path.js',
         ],
       },
+      {
+        type: 'js',
+        assets: [
+          'bundle-url.js',
+          'cacheLoader.js',
+          'import-polyfill.js',
+          'index.js',
+          'index.js',
+          'index.js',
+          'JSRuntime.js',
+          'JSRuntime.js',
+        ],
+      },
       {
         name: 'index.html',
         assets: ['index.html'],
@@ -1061,6 +1396,10 @@ describe('html', function() {
         type: 'js',
         assets: ['simpleHasher.js'],
       },
+      {
+        type: 'js',
+        assets: ['simpleHasher.js'],
+      },
     ]);
 
     let output = await run(b);
@@ -1116,16 +1455,11 @@ describe('html', function() {
       {
         type: 'js',
         assets: [
-          'bundle-manifest.js',
           'bundle-url.js',
-          'cacheLoader.js',
           'get-worker-url.js',
           'index.js',
-          'js-loader.js',
-          'JSRuntime.js',
           'JSRuntime.js',
           'JSRuntime.js',
-          'relative-path.js',
         ],
       },
       {
@@ -1177,16 +1511,11 @@ describe('html', function() {
       {
         type: 'js',
         assets: [
-          'bundle-manifest.js',
           'bundle-url.js',
-          'cacheLoader.js',
           'get-worker-url.js',
           'index.js',
-          'js-loader.js',
-          'JSRuntime.js',
           'JSRuntime.js',
           'JSRuntime.js',
-          'relative-path.js',
         ],
       },
       {
@@ -1281,7 +1610,13 @@ describe('html', function() {
         __dirname,
         'integration/scope-hoisting/es6/interop-async/index.html',
       ),
-      {production: true, scopeHoist: true},
+      {
+        production: true,
+        scopeHoist: true,
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
     );
     let bundles = b.getBundles();
 
diff --git a/packages/core/integration-tests/test/integration/blob-url/index.js b/packages/core/integration-tests/test/integration/blob-url/index.js
index da0b34b1b30..f2e66bdb274 100644
--- a/packages/core/integration-tests/test/integration/blob-url/index.js
+++ b/packages/core/integration-tests/test/integration/blob-url/index.js
@@ -1,2 +1,2 @@
-let worker = new Worker('blob-url:./worker');
+let worker = new Worker('blob-url:./worker', {type: 'module'});
 worker.postMessage('test');
diff --git a/packages/core/integration-tests/test/integration/cache/src/index.html b/packages/core/integration-tests/test/integration/cache/src/index.html
index 7241f3ef9ba..7f4005b6ffa 100644
--- a/packages/core/integration-tests/test/integration/cache/src/index.html
+++ b/packages/core/integration-tests/test/integration/cache/src/index.html
@@ -1,6 +1,6 @@
 <!doctype html>
 <html>
   <body>
-    <script src="index.js"></script>
+    <script type="module" src="index.js"></script>
   </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/child-bundle-different-types/index.html b/packages/core/integration-tests/test/integration/child-bundle-different-types/index.html
index 369affb5284..5d598792931 100644
--- a/packages/core/integration-tests/test/integration/child-bundle-different-types/index.html
+++ b/packages/core/integration-tests/test/integration/child-bundle-different-types/index.html
@@ -11,7 +11,7 @@
   <div id="main1">
     Hello World Main1
   </div>
-  <script src="./main.js"></script>
+  <script type="module" src="./main.js"></script>
   <a href="./other.html">GOOO</a>
 </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/child-bundle-different-types/other.html b/packages/core/integration-tests/test/integration/child-bundle-different-types/other.html
index 039877f1c75..f8f2fd35821 100644
--- a/packages/core/integration-tests/test/integration/child-bundle-different-types/other.html
+++ b/packages/core/integration-tests/test/integration/child-bundle-different-types/other.html
@@ -12,6 +12,6 @@
   <div id="main1">
     Heelo
   </div>
-  <script src="./index.js"></script>
+  <script type="module" src="./index.js"></script>
 </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/config-merging/node_modules/parcel-config-test1/index.json b/packages/core/integration-tests/test/integration/config-merging/node_modules/parcel-config-test1/index.json
index f5c63dad559..bd936f973cf 100644
--- a/packages/core/integration-tests/test/integration/config-merging/node_modules/parcel-config-test1/index.json
+++ b/packages/core/integration-tests/test/integration/config-merging/node_modules/parcel-config-test1/index.json
@@ -1,5 +1,3 @@
 {
-  "runtimes": {
-    "node": ["parcel-runtime-nothing"]
-  }
-}
\ No newline at end of file
+  "runtimes": ["parcel-runtime-nothing"]
+}
diff --git a/packages/core/integration-tests/test/integration/formats/esm-split-worker/index.html b/packages/core/integration-tests/test/integration/formats/esm-split-worker/index.html
index f9757275016..8ef9a70b216 100644
--- a/packages/core/integration-tests/test/integration/formats/esm-split-worker/index.html
+++ b/packages/core/integration-tests/test/integration/formats/esm-split-worker/index.html
@@ -1 +1 @@
-<script src="./index.js"></script>
+<script type="module" src="./index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/formats/global-split-worker/index.js b/packages/core/integration-tests/test/integration/formats/global-split-worker/index.js
index acd15616078..4e92121ae11 100644
--- a/packages/core/integration-tests/test/integration/formats/global-split-worker/index.js
+++ b/packages/core/integration-tests/test/integration/formats/global-split-worker/index.js
@@ -1 +1 @@
-new Worker("./main-worker");
+new Worker("./main-worker", {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/hmr-css/index.html b/packages/core/integration-tests/test/integration/hmr-css/index.html
index be258553b16..9c2debef441 100644
--- a/packages/core/integration-tests/test/integration/hmr-css/index.html
+++ b/packages/core/integration-tests/test/integration/hmr-css/index.html
@@ -6,6 +6,6 @@
 </head>
 <body>
   <h1>Hello world</h1>
-  <script src="index.js"></script>
+  <script type="module" src="index.js"></script>
 </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-css-doctype/index.html b/packages/core/integration-tests/test/integration/html-css-doctype/index.html
index 20089f80e97..621e1c3896c 100644
--- a/packages/core/integration-tests/test/integration/html-css-doctype/index.html
+++ b/packages/core/integration-tests/test/integration/html-css-doctype/index.html
@@ -1,2 +1,2 @@
 <!DOCTYPE html>
-<script src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-css-head/index.html b/packages/core/integration-tests/test/integration/html-css-head/index.html
index 4a75e1b2f68..73d78078aef 100644
--- a/packages/core/integration-tests/test/integration/html-css-head/index.html
+++ b/packages/core/integration-tests/test/integration/html-css-head/index.html
@@ -2,6 +2,6 @@
 <html>
 <body>
   <h1>Hello world</h1>
-  <script src="index.js"></script>
+  <script type="module" src="index.js"></script>
 </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-css-multi/index.html b/packages/core/integration-tests/test/integration/html-css-multi/index.html
index 96d3c5bc374..ffa2fe3ccf0 100644
--- a/packages/core/integration-tests/test/integration/html-css-multi/index.html
+++ b/packages/core/integration-tests/test/integration/html-css-multi/index.html
@@ -5,7 +5,7 @@
 </head>
 <body>
   <h1>Hello world</h1>
-  <script src="a.js"></script>
-  <script src="b.js"></script>
+  <script type="module" src="a.js"></script>
+  <script type="module" src="b.js"></script>
 </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-css-optional-elements/index.html b/packages/core/integration-tests/test/integration/html-css-optional-elements/index.html
index 5872bd0c236..daa2db4ff8c 100644
--- a/packages/core/integration-tests/test/integration/html-css-optional-elements/index.html
+++ b/packages/core/integration-tests/test/integration/html-css-optional-elements/index.html
@@ -1,3 +1,3 @@
-<script src="other.js"></script>
+<script type="module" src="other.js"></script>
 <h1>Hello world</h1>
-<script src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-css/index.html b/packages/core/integration-tests/test/integration/html-css/index.html
index 6c89ab7a5d1..d4fe22cfc3c 100644
--- a/packages/core/integration-tests/test/integration/html-css/index.html
+++ b/packages/core/integration-tests/test/integration/html-css/index.html
@@ -5,6 +5,6 @@
 </head>
 <body>
   <h1>Hello world</h1>
-  <script src="index.js"></script>
+  <script type="module" src="index.js"></script>
 </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-inline-js-nested/index.html b/packages/core/integration-tests/test/integration/html-inline-js-nested/index.html
index 9236b58d00c..2e5bfbe1c8d 100644
--- a/packages/core/integration-tests/test/integration/html-inline-js-nested/index.html
+++ b/packages/core/integration-tests/test/integration/html-inline-js-nested/index.html
@@ -1,7 +1,7 @@
 <!DOCTYPE html>
 <html>
 <body>
-  <script>
+  <script type="module">
     require('./test');
   </script>
 </body>
diff --git a/packages/core/integration-tests/test/integration/html-inline-js-require/index.html b/packages/core/integration-tests/test/integration/html-inline-js-require/index.html
index db239f85561..25491b16e20 100644
--- a/packages/core/integration-tests/test/integration/html-inline-js-require/index.html
+++ b/packages/core/integration-tests/test/integration/html-inline-js-require/index.html
@@ -1,7 +1,7 @@
 <!DOCTYPE html>
 <html>
 <body>
-  <script>
+  <script type="module">
     require('./test');
   </script>
 </body>
diff --git a/packages/core/integration-tests/test/integration/html-inline-js-script/error.html b/packages/core/integration-tests/test/integration/html-inline-js-script/error.html
new file mode 100644
index 00000000000..37ba6b5d52f
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/html-inline-js-script/error.html
@@ -0,0 +1,8 @@
+<!doctype html>
+<html>
+  <body>
+    <script>
+      import './module';
+    </script>
+  </body>
+</html>
diff --git a/packages/core/integration-tests/test/integration/html-inline-js-script/globals-dependencies.html b/packages/core/integration-tests/test/integration/html-inline-js-script/globals-dependencies.html
new file mode 100644
index 00000000000..5eb3d443626
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/html-inline-js-script/globals-dependencies.html
@@ -0,0 +1,34 @@
+<!doctype html>
+<html>
+  <body>
+    <script>
+      log(typeof bar, typeof baz);
+      let x = 2;
+      if (true) {
+        log(typeof bar, typeof baz);
+        let y = 3;
+        var z = 4;
+        function bar() {}
+        class Test {}
+      }
+
+      log(typeof bar, typeof baz);
+
+      class Foo {}
+      function baz() {}
+
+      import('./module');
+    </script>
+    <script>
+      output = {
+        x,
+        y: typeof y,
+        z,
+        bar,
+        Test: typeof Test,
+        Foo,
+        baz
+      };
+    </script>
+  </body>
+</html>
diff --git a/packages/core/integration-tests/test/integration/html-inline-js-script/globals.html b/packages/core/integration-tests/test/integration/html-inline-js-script/globals.html
new file mode 100644
index 00000000000..448885b5a46
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/html-inline-js-script/globals.html
@@ -0,0 +1,32 @@
+<!doctype html>
+<html>
+  <body>
+    <script>
+      log(typeof bar, typeof baz);
+      let x = 2;
+      if (true) {
+        log(typeof bar, typeof baz);
+        let y = 3;
+        var z = 4;
+        function bar() {}
+        class Test {}
+      }
+
+      log(typeof bar, typeof baz);
+
+      class Foo {}
+      function baz() {}
+    </script>
+    <script>
+      output = {
+        x,
+        y: typeof y,
+        z,
+        bar,
+        Test: typeof Test,
+        Foo,
+        baz
+      };
+    </script>
+  </body>
+</html>
diff --git a/packages/core/integration-tests/test/integration/html-inline-js-script/module.js b/packages/core/integration-tests/test/integration/html-inline-js-script/module.js
new file mode 100644
index 00000000000..e64329c055c
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/html-inline-js-script/module.js
@@ -0,0 +1 @@
+export function bar() {}
diff --git a/packages/core/integration-tests/test/integration/html-js-dedup/index.html b/packages/core/integration-tests/test/integration/html-js-dedup/index.html
index 9eb00fb7970..4f42abf403c 100644
--- a/packages/core/integration-tests/test/integration/html-js-dedup/index.html
+++ b/packages/core/integration-tests/test/integration/html-js-dedup/index.html
@@ -1,3 +1,3 @@
 <!DOCTYPE html>
-<script src="component-1.js"></script>
-<script src="component-2.js"></script>
+<script type="module" src="component-1.js"></script>
+<script type="module" src="component-2.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-js-dynamic/index.html b/packages/core/integration-tests/test/integration/html-js-dynamic/index.html
index 5b1eef45117..28a01ea786f 100644
--- a/packages/core/integration-tests/test/integration/html-js-dynamic/index.html
+++ b/packages/core/integration-tests/test/integration/html-js-dynamic/index.html
@@ -1 +1 @@
-<script src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-js-shared-dynamic-nested/index.html b/packages/core/integration-tests/test/integration/html-js-shared-dynamic-nested/index.html
index 62550945d54..28a01ea786f 100644
--- a/packages/core/integration-tests/test/integration/html-js-shared-dynamic-nested/index.html
+++ b/packages/core/integration-tests/test/integration/html-js-shared-dynamic-nested/index.html
@@ -1 +1 @@
-<script type="text/javascript" src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-js-shared-head/index.html b/packages/core/integration-tests/test/integration/html-js-shared-head/index.html
index de142808b50..574253d85c3 100644
--- a/packages/core/integration-tests/test/integration/html-js-shared-head/index.html
+++ b/packages/core/integration-tests/test/integration/html-js-shared-head/index.html
@@ -1,5 +1,5 @@
 <html>
   <head>
-    <script type="text/javascript" src="index.js"></script>
+    <script type="module" src="index.js"></script>
   </head>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-js-shared-head/index.js b/packages/core/integration-tests/test/integration/html-js-shared-head/index.js
index a6c38c90611..e4634b835fe 100644
--- a/packages/core/integration-tests/test/integration/html-js-shared-head/index.js
+++ b/packages/core/integration-tests/test/integration/html-js-shared-head/index.js
@@ -1,3 +1,3 @@
 console.log(require("lodash").add(1, 2));
 import("./async.js");
-new Worker("./worker.js");
+new Worker("./worker.js", {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/html-js-shared/index.html b/packages/core/integration-tests/test/integration/html-js-shared/index.html
index 62550945d54..28a01ea786f 100644
--- a/packages/core/integration-tests/test/integration/html-js-shared/index.html
+++ b/packages/core/integration-tests/test/integration/html-js-shared/index.html
@@ -1 +1 @@
-<script type="text/javascript" src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-js-shared/index.js b/packages/core/integration-tests/test/integration/html-js-shared/index.js
index a6c38c90611..e4634b835fe 100644
--- a/packages/core/integration-tests/test/integration/html-js-shared/index.js
+++ b/packages/core/integration-tests/test/integration/html-js-shared/index.js
@@ -1,3 +1,3 @@
 console.log(require("lodash").add(1, 2));
 import("./async.js");
-new Worker("./worker.js");
+new Worker("./worker.js", {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/html-js/error.html b/packages/core/integration-tests/test/integration/html-js/error.html
new file mode 100644
index 00000000000..5b1eef45117
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/html-js/error.html
@@ -0,0 +1 @@
+<script src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-js/index.html b/packages/core/integration-tests/test/integration/html-js/index.html
index 5b1eef45117..28a01ea786f 100644
--- a/packages/core/integration-tests/test/integration/html-js/index.html
+++ b/packages/core/integration-tests/test/integration/html-js/index.html
@@ -1 +1 @@
-<script src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/html-multi-entry/a.html b/packages/core/integration-tests/test/integration/html-multi-entry/a.html
index 3adf1b06490..cf0f457dce2 100644
--- a/packages/core/integration-tests/test/integration/html-multi-entry/a.html
+++ b/packages/core/integration-tests/test/integration/html-multi-entry/a.html
@@ -3,5 +3,5 @@
 </head>
 
 <body>
-	<script src="./index.js"></script>
+	<script type="module" src="./index.js"></script>
 </body>
\ No newline at end of file
diff --git a/packages/core/integration-tests/test/integration/html-multi-entry/b.html b/packages/core/integration-tests/test/integration/html-multi-entry/b.html
index 3adf1b06490..cf0f457dce2 100644
--- a/packages/core/integration-tests/test/integration/html-multi-entry/b.html
+++ b/packages/core/integration-tests/test/integration/html-multi-entry/b.html
@@ -3,5 +3,5 @@
 </head>
 
 <body>
-	<script src="./index.js"></script>
+	<script type="module" src="./index.js"></script>
 </body>
\ No newline at end of file
diff --git a/packages/core/integration-tests/test/integration/html-root/index.html b/packages/core/integration-tests/test/integration/html-root/index.html
index a060a6f8ece..8ef8c1c244b 100644
--- a/packages/core/integration-tests/test/integration/html-root/index.html
+++ b/packages/core/integration-tests/test/integration/html-root/index.html
@@ -5,6 +5,6 @@
 </head>
 <body>
   <a href="./other.html">goto page2</a>
-  <script type="text/javascript" src="./main.js"></script>
+  <script type="module" src="./main.js"></script>
 </body>
 </html>
\ No newline at end of file
diff --git a/packages/core/integration-tests/test/integration/html-root/other.html b/packages/core/integration-tests/test/integration/html-root/other.html
index 98159107ce9..0a3d424c585 100644
--- a/packages/core/integration-tests/test/integration/html-root/other.html
+++ b/packages/core/integration-tests/test/integration/html-root/other.html
@@ -5,6 +5,6 @@
 </head>
 <body>
   <a href="./index.html">goto page1</a>
-  <script type="text/javascript" src="./index2.js"></script>
+  <script type="module" src="./index2.js"></script>
 </body>
 </html>
\ No newline at end of file
diff --git a/packages/core/integration-tests/test/integration/html-shared-worker/index.html b/packages/core/integration-tests/test/integration/html-shared-worker/index.html
index 8de9044b9f0..adf50f053d1 100644
--- a/packages/core/integration-tests/test/integration/html-shared-worker/index.html
+++ b/packages/core/integration-tests/test/integration/html-shared-worker/index.html
@@ -2,6 +2,6 @@
 <html>
   <body>
     <h1>Hello!</h1>
-    <script src="./index.js"></script>
+    <script type="module" src="./index.js"></script>
   </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-shared-worker/index.js b/packages/core/integration-tests/test/integration/html-shared-worker/index.js
index 7cbc0d82094..b4357ed68aa 100644
--- a/packages/core/integration-tests/test/integration/html-shared-worker/index.js
+++ b/packages/core/integration-tests/test/integration/html-shared-worker/index.js
@@ -2,4 +2,4 @@ import _ from 'lodash';
 
 output("main", _.add(1, 2));
 
-new Worker('worker.js');
+new Worker('worker.js', {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/html-shared/iframe.html b/packages/core/integration-tests/test/integration/html-shared/iframe.html
index 98d8b81bdb8..82f21258c76 100644
--- a/packages/core/integration-tests/test/integration/html-shared/iframe.html
+++ b/packages/core/integration-tests/test/integration/html-shared/iframe.html
@@ -1,6 +1,6 @@
 <!doctype html>
 <html>
   <body>
-    <script src="iframe.js"></script>
+    <script type="module" src="iframe.js"></script>
   </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/html-shared/index.html b/packages/core/integration-tests/test/integration/html-shared/index.html
index d22e4819f68..807387c3516 100644
--- a/packages/core/integration-tests/test/integration/html-shared/index.html
+++ b/packages/core/integration-tests/test/integration/html-shared/index.html
@@ -3,6 +3,6 @@
   <body>
     <h1>Hello!</h1>
     <iframe src="iframe.html"></iframe>
-    <script src="./index.js"></script>
+    <script type="module" src="./index.js"></script>
   </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/react-refresh-lazy-child/index.html b/packages/core/integration-tests/test/integration/react-refresh-lazy-child/index.html
index fb38e86b2a2..4c99f276ba5 100644
--- a/packages/core/integration-tests/test/integration/react-refresh-lazy-child/index.html
+++ b/packages/core/integration-tests/test/integration/react-refresh-lazy-child/index.html
@@ -1,2 +1,2 @@
 <div id="root"></div>
-<script src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/react-refresh/index.html b/packages/core/integration-tests/test/integration/react-refresh/index.html
index fb38e86b2a2..4c99f276ba5 100644
--- a/packages/core/integration-tests/test/integration/react-refresh/index.html
+++ b/packages/core/integration-tests/test/integration/react-refresh/index.html
@@ -1,2 +1,2 @@
 <div id="root"></div>
-<script src="index.js"></script>
+<script type="module" src="index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/resolver-dependency-meta/.parcelrc b/packages/core/integration-tests/test/integration/resolver-dependency-meta/.parcelrc
index d17352e86fe..8010d0f9604 100644
--- a/packages/core/integration-tests/test/integration/resolver-dependency-meta/.parcelrc
+++ b/packages/core/integration-tests/test/integration/resolver-dependency-meta/.parcelrc
@@ -1,7 +1,5 @@
 {
   "extends": "@parcel/config-default",
   "resolvers": ["parcel-resolver-meta", "..."],
-  "runtimes": {
-    "browser": ["parcel-runtime-meta", "..."]
-  }
+  "runtimes": ["parcel-runtime-meta", "..."]
 }
diff --git a/packages/core/integration-tests/test/integration/runtime-symbol-merging/.parcelrc b/packages/core/integration-tests/test/integration/runtime-symbol-merging/.parcelrc
index 011e986fafe..596c8254b81 100644
--- a/packages/core/integration-tests/test/integration/runtime-symbol-merging/.parcelrc
+++ b/packages/core/integration-tests/test/integration/runtime-symbol-merging/.parcelrc
@@ -1,8 +1,6 @@
 {
   "extends": "@parcel/config-default",
-  "runtimes": {
-    "browser": [
-      "parcel-runtime-mock"
-    ]
-  }
+  "runtimes": [
+    "parcel-runtime-mock"
+  ]
 }
diff --git a/packages/core/integration-tests/test/integration/runtime-update/.parcelrc b/packages/core/integration-tests/test/integration/runtime-update/.parcelrc
index 44f2409a9d6..2faf969746e 100644
--- a/packages/core/integration-tests/test/integration/runtime-update/.parcelrc
+++ b/packages/core/integration-tests/test/integration/runtime-update/.parcelrc
@@ -1,8 +1,6 @@
 {
   "extends": "@parcel/config-default",
-  "runtimes": {
-    "browser": [
-      "parcel-runtime-mock",
-    ],
-  }
+  "runtimes": [
+    "parcel-runtime-mock",
+  ]
 }
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/interop-async/index.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/interop-async/index.html
index f9757275016..8ef9a70b216 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/interop-async/index.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/interop-async/index.html
@@ -1 +1 @@
-<script src="./index.js"></script>
+<script type="module" src="./index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/a.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/a.html
index ed52c3deec6..ee620ca3160 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/a.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/a.html
@@ -1 +1 @@
-<script src="a.js"></script>
+<script type="module" src="a.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/b.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/b.html
index f5c7be245a2..e1c1a4b209c 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/b.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/live-bindings-cross-bundle/b.html
@@ -1 +1 @@
-<script src="b.js"></script>
+<script type="module" src="b.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index1.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index1.html
index e4a8cdb478d..befa6f91239 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index1.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index1.html
@@ -1 +1 @@
-<script src="index1.js"></script>
+<script type="module" src="index1.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index2.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index2.html
index 4dadd38abaa..edbd81997e9 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index2.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index2.html
@@ -1 +1 @@
-<script src="index2.js"></script>
+<script type="module" src="index2.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index3.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index3.html
index 4f42e2ac316..a51fc0ab954 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index3.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/shared-bundle-reexport/index3.html
@@ -1 +1 @@
-<script src="index3.js"></script>
+<script type="module" src="index3.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-css/index.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-css/index.html
index 0053d2e2e7b..e244c5b18eb 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-css/index.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-css/index.html
@@ -1,2 +1,2 @@
 <div id="react-root"></div>
-<script src="./index.js"></script>
+<script type="module" src="./index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-no-new-bundle/index.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-no-new-bundle/index.html
index 0053d2e2e7b..e244c5b18eb 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-no-new-bundle/index.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-no-new-bundle/index.html
@@ -1,2 +1,2 @@
 <div id="react-root"></div>
-<script src="./index.js"></script>
+<script type="module" src="./index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/update-used-symbols-dependency-add-namespace/index.html b/packages/core/integration-tests/test/integration/scope-hoisting/es6/update-used-symbols-dependency-add-namespace/index.html
index 0053d2e2e7b..e244c5b18eb 100644
--- a/packages/core/integration-tests/test/integration/scope-hoisting/es6/update-used-symbols-dependency-add-namespace/index.html
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/update-used-symbols-dependency-add-namespace/index.html
@@ -1,2 +1,2 @@
 <div id="react-root"></div>
-<script src="./index.js"></script>
+<script type="module" src="./index.js"></script>
diff --git a/packages/core/integration-tests/test/integration/service-worker/error.js b/packages/core/integration-tests/test/integration/service-worker/error.js
new file mode 100644
index 00000000000..1c2367a89e1
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/service-worker/error.js
@@ -0,0 +1 @@
+navigator.serviceWorker.register('module-worker.js');
diff --git a/packages/core/integration-tests/test/integration/service-worker/module-worker.js b/packages/core/integration-tests/test/integration/service-worker/module-worker.js
new file mode 100644
index 00000000000..2263b5a27c2
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/service-worker/module-worker.js
@@ -0,0 +1 @@
+export var foo = 2;
diff --git a/packages/core/integration-tests/test/integration/service-worker/module.js b/packages/core/integration-tests/test/integration/service-worker/module.js
new file mode 100644
index 00000000000..d9f4432c70a
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/service-worker/module.js
@@ -0,0 +1 @@
+navigator.serviceWorker.register('module-worker.js', {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/service-worker/scope.js b/packages/core/integration-tests/test/integration/service-worker/scope.js
new file mode 100644
index 00000000000..a0508f2fa4d
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/service-worker/scope.js
@@ -0,0 +1 @@
+navigator.serviceWorker.register('module-worker.js', {scope: 'foo', type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/shared-many/a.html b/packages/core/integration-tests/test/integration/shared-many/a.html
index cb28dbc1313..6903d403236 100644
--- a/packages/core/integration-tests/test/integration/shared-many/a.html
+++ b/packages/core/integration-tests/test/integration/shared-many/a.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="a.js"></script>
+<script type="module" src="a.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-many/b.html b/packages/core/integration-tests/test/integration/shared-many/b.html
index 44f7261b512..2bc0b3c2f66 100644
--- a/packages/core/integration-tests/test/integration/shared-many/b.html
+++ b/packages/core/integration-tests/test/integration/shared-many/b.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="b.js"></script>
+<script type="module" src="b.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-many/c.html b/packages/core/integration-tests/test/integration/shared-many/c.html
index ef94f9e2e62..d2a95cd1392 100644
--- a/packages/core/integration-tests/test/integration/shared-many/c.html
+++ b/packages/core/integration-tests/test/integration/shared-many/c.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="c.js"></script>
+<script type="module" src="c.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-many/d.html b/packages/core/integration-tests/test/integration/shared-many/d.html
index c4e8e75143f..b5cb0558627 100644
--- a/packages/core/integration-tests/test/integration/shared-many/d.html
+++ b/packages/core/integration-tests/test/integration/shared-many/d.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="d.js"></script>
+<script type="module" src="d.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-many/e.html b/packages/core/integration-tests/test/integration/shared-many/e.html
index f1294f1c7ce..2792f4f3428 100644
--- a/packages/core/integration-tests/test/integration/shared-many/e.html
+++ b/packages/core/integration-tests/test/integration/shared-many/e.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="e.js"></script>
+<script type="module" src="e.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-many/f.html b/packages/core/integration-tests/test/integration/shared-many/f.html
index 967f3cdc4a3..e7d8a3a8890 100644
--- a/packages/core/integration-tests/test/integration/shared-many/f.html
+++ b/packages/core/integration-tests/test/integration/shared-many/f.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="f.js"></script>
+<script type="module" src="f.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-many/g.html b/packages/core/integration-tests/test/integration/shared-many/g.html
index bc01514e1d5..aacfc6ae995 100644
--- a/packages/core/integration-tests/test/integration/shared-many/g.html
+++ b/packages/core/integration-tests/test/integration/shared-many/g.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="g.js"></script>
+<script type="module" src="g.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-sibling-duplicate/a.html b/packages/core/integration-tests/test/integration/shared-sibling-duplicate/a.html
index cb28dbc1313..6903d403236 100644
--- a/packages/core/integration-tests/test/integration/shared-sibling-duplicate/a.html
+++ b/packages/core/integration-tests/test/integration/shared-sibling-duplicate/a.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="a.js"></script>
+<script type="module" src="a.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-sibling-duplicate/b.html b/packages/core/integration-tests/test/integration/shared-sibling-duplicate/b.html
index 44f7261b512..2bc0b3c2f66 100644
--- a/packages/core/integration-tests/test/integration/shared-sibling-duplicate/b.html
+++ b/packages/core/integration-tests/test/integration/shared-sibling-duplicate/b.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="b.js"></script>
+<script type="module" src="b.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-sibling-duplicate/c.html b/packages/core/integration-tests/test/integration/shared-sibling-duplicate/c.html
index ef94f9e2e62..d2a95cd1392 100644
--- a/packages/core/integration-tests/test/integration/shared-sibling-duplicate/c.html
+++ b/packages/core/integration-tests/test/integration/shared-sibling-duplicate/c.html
@@ -1,2 +1,2 @@
 <!doctype html>
-<script src="c.js"></script>
+<script type="module" src="c.js"></script>
diff --git a/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/a.html b/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/a.html
index b7ba0a892bf..89f54f613d6 100644
--- a/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/a.html
+++ b/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/a.html
@@ -2,6 +2,6 @@
 <html>
   <body>
     <h1>a.html</h1>
-    <script src="./a.js"></script>
+    <script type="module" src="./a.js"></script>
   </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/b.html b/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/b.html
index e2a24e1af0b..ff2bfebf4ac 100644
--- a/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/b.html
+++ b/packages/core/integration-tests/test/integration/shared-sibling-entries-multiple/b.html
@@ -2,6 +2,6 @@
 <html>
   <body>
     <h1>b.html</h1>
-    <script src="./b.js"></script>
+    <script type="module" src="./b.js"></script>
   </body>
 </html>
diff --git a/packages/core/integration-tests/test/integration/worker-circular/index.js b/packages/core/integration-tests/test/integration/worker-circular/index.js
index c25bcacc792..356faefd8bd 100644
--- a/packages/core/integration-tests/test/integration/worker-circular/index.js
+++ b/packages/core/integration-tests/test/integration/worker-circular/index.js
@@ -1 +1 @@
-new Worker('worker.js');
+new Worker('worker.js', {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/worker-shared/index.js b/packages/core/integration-tests/test/integration/worker-shared/index.js
index 2be98ad89c5..1033f7abd70 100644
--- a/packages/core/integration-tests/test/integration/worker-shared/index.js
+++ b/packages/core/integration-tests/test/integration/worker-shared/index.js
@@ -1,3 +1,3 @@
 import _ from 'lodash';
 
-new Worker('worker-a.js');
+new Worker('worker-a.js', {type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/worker-shared/worker-a.js b/packages/core/integration-tests/test/integration/worker-shared/worker-a.js
index f1e1cc07cf1..905ce5bbd0a 100644
--- a/packages/core/integration-tests/test/integration/worker-shared/worker-a.js
+++ b/packages/core/integration-tests/test/integration/worker-shared/worker-a.js
@@ -1,4 +1,4 @@
 import _ from 'lodash'
 
 console.log(_);
-new Worker('worker-b.js')
+new Worker('worker-b.js', {type: 'module'})
diff --git a/packages/core/integration-tests/test/integration/workers-module/dedicated-worker.js b/packages/core/integration-tests/test/integration/workers-module/dedicated-worker.js
index 52946114304..0881af7c961 100644
--- a/packages/core/integration-tests/test/integration/workers-module/dedicated-worker.js
+++ b/packages/core/integration-tests/test/integration/workers-module/dedicated-worker.js
@@ -1,3 +1,4 @@
 import foo from "foo";
 
 console.log("DedicatedWorker", foo);
+export {foo};
diff --git a/packages/core/integration-tests/test/integration/workers-module/error.js b/packages/core/integration-tests/test/integration/workers-module/error.js
new file mode 100644
index 00000000000..4d606f86efd
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/workers-module/error.js
@@ -0,0 +1 @@
+new Worker("dedicated-worker.js");
diff --git a/packages/core/integration-tests/test/integration/workers-module/named.js b/packages/core/integration-tests/test/integration/workers-module/named.js
new file mode 100644
index 00000000000..3dc9f858ef4
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/workers-module/named.js
@@ -0,0 +1,2 @@
+new Worker("dedicated-worker.js", {name: 'worker', type: 'module'});
+new SharedWorker("shared-worker.js", {name: 'shared', type: 'module'});
diff --git a/packages/core/integration-tests/test/integration/workers-module/package.json b/packages/core/integration-tests/test/integration/workers-module/package.json
deleted file mode 100644
index 33859c5e19d..00000000000
--- a/packages/core/integration-tests/test/integration/workers-module/package.json
+++ /dev/null
@@ -1,7 +0,0 @@
-{
-    "targets": {
-        "default": {
-            "includeNodeModules": false
-        }
-    }
-}
diff --git a/packages/core/integration-tests/test/integration/workers-module/shared-worker.js b/packages/core/integration-tests/test/integration/workers-module/shared-worker.js
index 91f7355fdd9..becc2ed02a9 100644
--- a/packages/core/integration-tests/test/integration/workers-module/shared-worker.js
+++ b/packages/core/integration-tests/test/integration/workers-module/shared-worker.js
@@ -1,3 +1,4 @@
 import foo from "foo";
 
 console.log("SharedWorker", foo);
+export {foo};
diff --git a/packages/core/integration-tests/test/integration/workers/worker-client.js b/packages/core/integration-tests/test/integration/workers/worker-client.js
index 4c37977e839..c7b3189ebf4 100644
--- a/packages/core/integration-tests/test/integration/workers/worker-client.js
+++ b/packages/core/integration-tests/test/integration/workers/worker-client.js
@@ -3,12 +3,12 @@ const commonText = require('./common').commonFunction('Index');
 navigator.serviceWorker.register('service-worker.js', { scope: './' });
 
 exports.startWorker = function() {
-  const worker = new Worker('worker.js', {name: 'myName'});
+  const worker = new Worker('worker.js', {type: 'module', name: 'myName'});
   worker.postMessage(commonText);
 };
 
 exports.startSharedWorker = function() {
-  const worker = new SharedWorker('shared-worker.js');
+  const worker = new SharedWorker('shared-worker.js', {type: 'module'});
 };
 
 
diff --git a/packages/core/integration-tests/test/javascript.js b/packages/core/integration-tests/test/javascript.js
index bab7c97f4f5..9938959cf3b 100644
--- a/packages/core/integration-tests/test/javascript.js
+++ b/packages/core/integration-tests/test/javascript.js
@@ -541,7 +541,7 @@ describe('javascript', function() {
 
     assertBundles(b, [
       {
-        assets: ['dedicated-worker.js'],
+        assets: ['dedicated-worker.js', 'index.js'],
       },
       {
         name: 'index.js',
@@ -557,7 +557,7 @@ describe('javascript', function() {
         ],
       },
       {
-        assets: ['shared-worker.js'],
+        assets: ['shared-worker.js', 'index.js'],
       },
     ]);
 
@@ -576,10 +576,155 @@ describe('javascript', function() {
     assert(dedicated);
     assert(shared);
 
+    let main = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
     dedicated = await outputFS.readFile(dedicated.filePath, 'utf8');
     shared = await outputFS.readFile(shared.filePath, 'utf8');
-    assert(/import .* from ?"foo";/.test(dedicated));
-    assert(/import .* from ?"foo";/.test(shared));
+    assert(/new Worker(.*?, {[\n\s]+type: 'module'[\n\s]+})/.test(main));
+    assert(/new SharedWorker(.*?, {[\n\s]+type: 'module'[\n\s]+})/.test(main));
+    assert(/export var foo/.test(dedicated));
+    assert(/export var foo/.test(shared));
+  });
+
+  for (let scopeHoist of [true, false]) {
+    it(`should compile workers to non modules if ${
+      scopeHoist ? 'browsers do not support it' : 'scopeHoist = false'
+    }`, async function() {
+      let b = await bundle(
+        path.join(__dirname, '/integration/workers-module/index.js'),
+        {
+          scopeHoist,
+          defaultEngines: {
+            browsers: '>= 0.25%',
+          },
+        },
+      );
+
+      assertBundles(b, [
+        {
+          assets: ['dedicated-worker.js', 'index.js'],
+        },
+        {
+          name: 'index.js',
+          assets: [
+            'index.js',
+            'bundle-url.js',
+            'JSRuntime.js',
+            'JSRuntime.js',
+            'JSRuntime.js',
+            'get-worker-url.js',
+            'bundle-manifest.js',
+            'relative-path.js',
+          ],
+        },
+        {
+          assets: ['shared-worker.js', 'index.js'],
+        },
+      ]);
+
+      let dedicated, shared;
+      b.traverseBundles((bundle, ctx, traversal) => {
+        if (bundle.getMainEntry().filePath.endsWith('shared-worker.js')) {
+          shared = bundle;
+        } else if (
+          bundle.getMainEntry().filePath.endsWith('dedicated-worker.js')
+        ) {
+          dedicated = bundle;
+        }
+        if (dedicated && shared) traversal.stop();
+      });
+
+      assert(dedicated);
+      assert(shared);
+
+      let main = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+      dedicated = await outputFS.readFile(dedicated.filePath, 'utf8');
+      shared = await outputFS.readFile(shared.filePath, 'utf8');
+      assert(/new Worker([^,]*?)/.test(main));
+      assert(/new SharedWorker([^,]*?)/.test(main));
+      assert(!/export var foo/.test(dedicated));
+      assert(!/export var foo/.test(shared));
+    });
+  }
+
+  it('should preserve the name option to workers', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/workers-module/named.js'),
+      {
+        scopeHoist: true,
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
+    );
+
+    let main = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+    assert(/new Worker(.*?, {[\n\s]+name: 'worker'[\n\s]+})/.test(main));
+    assert(/new SharedWorker(.*?, {[\n\s]+name: 'shared'[\n\s]+})/.test(main));
+  });
+
+  it('should error if importing in a worker without type: module', async function() {
+    let errored = false;
+    try {
+      await bundle(
+        path.join(__dirname, '/integration/workers-module/error.js'),
+        {scopeHoist: true},
+      );
+    } catch (err) {
+      errored = true;
+      assert.equal(
+        err.message,
+        'Web workers cannot have imports or exports. Use the `type: "module"` option instead.',
+      );
+      assert.deepEqual(err.diagnostics, [
+        {
+          message:
+            'Web workers cannot have imports or exports. Use the `type: "module"` option instead.',
+          filePath: path.join(
+            __dirname,
+            '/integration/workers-module/dedicated-worker.js',
+          ),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 1,
+                  column: 1,
+                },
+                end: {
+                  line: 1,
+                  column: 22,
+                },
+              },
+            ],
+          },
+        },
+        {
+          message: 'The environment was originally created here:',
+          filePath: path.join(
+            __dirname,
+            '/integration/workers-module/error.js',
+          ),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 1,
+                  column: 1,
+                },
+                end: {
+                  line: 1,
+                  column: 33,
+                },
+              },
+            ],
+          },
+        },
+      ]);
+    }
+
+    assert(errored);
   });
 
   it('should support bundling workers with different order', async function() {
@@ -756,6 +901,136 @@ describe('javascript', function() {
     ]);
   });
 
+  it('should support bundling service-workers with type: module', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/service-worker/module.js'),
+      {scopeHoist: true},
+    );
+
+    assertBundles(b, [
+      {
+        name: 'module.js',
+        assets: [
+          'module.js',
+          'bundle-url.js',
+          'JSRuntime.js',
+          'JSRuntime.js',
+          'bundle-manifest.js',
+          'relative-path.js',
+        ],
+      },
+      {
+        assets: ['module-worker.js'],
+      },
+    ]);
+
+    let bundles = b.getBundles();
+    let main = bundles.find(b => !b.env.isWorker());
+    let worker = bundles.find(b => b.env.isWorker());
+    let mainContents = await outputFS.readFile(main.filePath, 'utf8');
+    let workerContents = await outputFS.readFile(worker.filePath, 'utf8');
+    assert(/navigator.serviceWorker.register\([^,]+?\)/.test(mainContents));
+    assert(!/export/.test(workerContents));
+  });
+
+  it('should preserve the scope option for service workers', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/service-worker/scope.js'),
+      {scopeHoist: true},
+    );
+
+    assertBundles(b, [
+      {
+        name: 'scope.js',
+        assets: [
+          'scope.js',
+          'bundle-url.js',
+          'JSRuntime.js',
+          'JSRuntime.js',
+          'bundle-manifest.js',
+          'relative-path.js',
+        ],
+      },
+      {
+        assets: ['module-worker.js'],
+      },
+    ]);
+
+    let bundles = b.getBundles();
+    let main = bundles.find(b => !b.env.isWorker());
+    let mainContents = await outputFS.readFile(main.filePath, 'utf8');
+    assert(
+      /navigator.serviceWorker.register\(.*?, {[\n\s]*scope: 'foo'[\n\s]*}\)/.test(
+        mainContents,
+      ),
+    );
+  });
+
+  it('should error if importing in a service worker without type: module', async function() {
+    let errored = false;
+    try {
+      await bundle(
+        path.join(__dirname, '/integration/service-worker/error.js'),
+        {scopeHoist: true},
+      );
+    } catch (err) {
+      errored = true;
+      assert.equal(
+        err.message,
+        'Service workers cannot have imports or exports. Use the `type: "module"` option instead.',
+      );
+      assert.deepEqual(err.diagnostics, [
+        {
+          message:
+            'Service workers cannot have imports or exports. Use the `type: "module"` option instead.',
+          filePath: path.join(
+            __dirname,
+            '/integration/service-worker/module-worker.js',
+          ),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 1,
+                  column: 1,
+                },
+                end: {
+                  line: 1,
+                  column: 19,
+                },
+              },
+            ],
+          },
+        },
+        {
+          message: 'The environment was originally created here:',
+          filePath: path.join(
+            __dirname,
+            '/integration/service-worker/error.js',
+          ),
+          origin: '@parcel/transformer-js',
+          codeFrame: {
+            codeHighlights: [
+              {
+                start: {
+                  line: 1,
+                  column: 1,
+                },
+                end: {
+                  line: 1,
+                  column: 52,
+                },
+              },
+            ],
+          },
+        },
+      ]);
+    }
+
+    assert(errored);
+  });
+
   it('should support bundling workers with circular dependencies', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/worker-circular/index.js'),
diff --git a/packages/core/integration-tests/test/output-formats.js b/packages/core/integration-tests/test/output-formats.js
index 096540616af..747b1b5a72a 100644
--- a/packages/core/integration-tests/test/output-formats.js
+++ b/packages/core/integration-tests/test/output-formats.js
@@ -832,7 +832,7 @@ describe('output formats', function() {
       );
 
       let workerBundle = nullthrows(
-        b.getBundles().find(b => b.env.context === 'web-worker'),
+        b.getBundles().find(b => b.env.context.has('web-worker')),
       );
       let workerBundleContents = await outputFS.readFile(
         workerBundle.filePath,
diff --git a/packages/core/integration-tests/test/scope-hoisting.js b/packages/core/integration-tests/test/scope-hoisting.js
index f6f6420c075..2dedbfe9a30 100644
--- a/packages/core/integration-tests/test/scope-hoisting.js
+++ b/packages/core/integration-tests/test/scope-hoisting.js
@@ -502,6 +502,11 @@ describe('scope hoisting', function() {
             f,
           ),
         ),
+        {
+          defaultEngines: {
+            browsers: '>= 0.25%',
+          },
+        },
       );
 
       let output = await runBundle(
@@ -824,6 +829,11 @@ describe('scope hoisting', function() {
           __dirname,
           '/integration/scope-hoisting/es6/shared-bundle-reexport/*.html',
         ),
+        {
+          defaultEngines: {
+            browsers: '>= 0.25%',
+          },
+        },
       );
 
       assertBundles(b, [
@@ -835,6 +845,10 @@ describe('scope hoisting', function() {
           type: 'js',
           assets: ['index1.js'],
         },
+        {
+          type: 'js',
+          assets: ['index1.js'],
+        },
         {
           type: 'html',
           assets: ['index2.html'],
@@ -843,6 +857,10 @@ describe('scope hoisting', function() {
           type: 'js',
           assets: ['index2.js'],
         },
+        {
+          type: 'js',
+          assets: ['index2.js'],
+        },
         {
           type: 'html',
           assets: ['index3.html'],
@@ -851,10 +869,22 @@ describe('scope hoisting', function() {
           type: 'js',
           assets: ['index3.js'],
         },
+        {
+          type: 'js',
+          assets: ['index3.js'],
+        },
         {
           type: 'js',
           assets: ['a.js'],
         },
+        {
+          type: 'js',
+          assets: ['a.js'],
+        },
+        {
+          type: 'js',
+          assets: ['b.js'],
+        },
         {
           type: 'js',
           assets: ['b.js'],
@@ -1681,6 +1711,11 @@ describe('scope hoisting', function() {
           __dirname,
           '/integration/scope-hoisting/es6/interop-async/index.html',
         ),
+        {
+          defaultEngines: {
+            browsers: '>= 0.25%',
+          },
+        },
       );
 
       let output = await run(b);
@@ -2033,6 +2068,9 @@ describe('scope hoisting', function() {
         let b = bundler(path.join(testDir, 'index.html'), {
           inputFS: overlayFS,
           outputFS: overlayFS,
+          defaultEngines: {
+            browsers: '>= 0.25%',
+          },
         });
 
         await overlayFS.mkdirp(testDir);
@@ -2148,6 +2186,11 @@ describe('scope hoisting', function() {
             __dirname,
             '/integration/scope-hoisting/es6/side-effects-css/index.html',
           ),
+          {
+            defaultEngines: {
+              browsers: '>= 0.25%',
+            },
+          },
         );
 
         assertBundles(b, [
@@ -2159,6 +2202,10 @@ describe('scope hoisting', function() {
             type: 'js',
             assets: ['index.js', 'a.js', 'b1.js'],
           },
+          {
+            type: 'js',
+            assets: ['index.js', 'a.js', 'b1.js'],
+          },
           {
             type: 'css',
             assets: ['b1.css'],
@@ -2187,6 +2234,7 @@ describe('scope hoisting', function() {
             __dirname,
             '/integration/scope-hoisting/es6/side-effects-no-new-bundle/index.html',
           ),
+          {defaultEngines: {browsers: '>= 0.25%'}},
         );
 
         assertBundles(b, [
@@ -2198,6 +2246,10 @@ describe('scope hoisting', function() {
             type: 'js',
             assets: ['index.js', 'a.js', 'b1.js'],
           },
+          {
+            type: 'js',
+            assets: ['index.js', 'a.js', 'b1.js'],
+          },
         ]);
 
         let calls = [];
@@ -4133,6 +4185,11 @@ describe('scope hoisting', function() {
   it('should not throw with JS included from HTML', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/html-js/index.html'),
+      {
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
     );
 
     assertBundles(b, [
@@ -4144,6 +4201,10 @@ describe('scope hoisting', function() {
         type: 'js',
         assets: ['index.js', 'other.js'],
       },
+      {
+        type: 'js',
+        assets: ['index.js', 'other.js'],
+      },
     ]);
 
     let asset = nullthrows(findAsset(b, 'other.js'));
@@ -4162,6 +4223,11 @@ describe('scope hoisting', function() {
   it('should not throw with JS dynamic imports included from HTML', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/html-js-dynamic/index.html'),
+      {
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
     );
 
     assertBundles(b, [
@@ -4182,6 +4248,20 @@ describe('scope hoisting', function() {
           'relative-path.js',
         ],
       },
+      {
+        type: 'js',
+        assets: [
+          'bundle-url.js',
+          'cacheLoader.js',
+          'import-polyfill.js',
+          'index.js',
+          'JSRuntime.js',
+        ],
+      },
+      {
+        type: 'js',
+        assets: ['local.js'],
+      },
       {
         type: 'js',
         assets: ['local.js'],
@@ -4196,6 +4276,11 @@ describe('scope hoisting', function() {
   it('should include the prelude in shared entry bundles', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/html-shared/index.html'),
+      {
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
     );
 
     assertBundles(b, [
@@ -4207,6 +4292,10 @@ describe('scope hoisting', function() {
         type: 'js',
         assets: ['index.js'],
       },
+      {
+        type: 'js',
+        assets: ['index.js'],
+      },
       {
         name: 'iframe.html',
         assets: ['iframe.html'],
@@ -4215,6 +4304,14 @@ describe('scope hoisting', function() {
         type: 'js',
         assets: ['iframe.js'],
       },
+      {
+        type: 'js',
+        assets: ['iframe.js'],
+      },
+      {
+        type: 'js',
+        assets: ['lodash.js'],
+      },
       {
         type: 'js',
         assets: ['lodash.js'],
@@ -4241,6 +4338,11 @@ describe('scope hoisting', function() {
   it('should include prelude in shared worker bundles', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/worker-shared/index.js'),
+      {
+        defaultEngines: {
+          browsers: '>= 0.25%',
+        },
+      },
     );
 
     let sharedBundle = b
diff --git a/packages/core/test-utils/package.json b/packages/core/test-utils/package.json
index cafdc5ce5e4..f23cae11ecd 100644
--- a/packages/core/test-utils/package.json
+++ b/packages/core/test-utils/package.json
@@ -13,6 +13,8 @@
     "node": ">= 10.0.0"
   },
   "dependencies": {
+    "@babel/core": "^7.12.0",
+    "@babel/plugin-transform-modules-commonjs": "^7.0.0",
     "@parcel/config-default": "2.0.0-beta.1",
     "@parcel/core": "2.0.0-beta.1",
     "@parcel/fs": "2.0.0-beta.1",
diff --git a/packages/core/test-utils/src/utils.js b/packages/core/test-utils/src/utils.js
index bc8ee28e03b..5b60d12aee2 100644
--- a/packages/core/test-utils/src/utils.js
+++ b/packages/core/test-utils/src/utils.js
@@ -29,6 +29,7 @@ import {makeDeferredWithPromise, normalizeSeparators} from '@parcel/utils';
 import _chalk from 'chalk';
 import resolve from 'resolve';
 import {NodePackageManager} from '@parcel/package-manager';
+import {transformSync} from '@babel/core';
 
 export const workerFarm = (createWorkerFarm(): WorkerFarm);
 export const inputFS: NodeFS = new NodeFS();
@@ -207,46 +208,82 @@ type RunOpts = {require?: boolean, ...};
 export async function runBundles(
   bundleGraph: BundleGraph<NamedBundle>,
   parent: NamedBundle,
-  bundles: Array<NamedBundle>,
+  bundles: Array<[string, NamedBundle]>,
   globals: mixed,
   opts: RunOpts = {},
 ): Promise<mixed> {
   let entryAsset = nullthrows(
     bundles
-      .map(b => b.getMainEntry() || b.getEntryAssets()[0])
+      .map(([, b]) => b.getMainEntry() || b.getEntryAssets()[0])
       .filter(Boolean)[0],
   );
   let env = entryAsset.env;
-  let target = entryAsset.env.context;
 
   let ctx, promises;
-  switch (target) {
-    case 'browser': {
-      let prepared = prepareBrowserContext(parent.filePath, globals);
-      ctx = prepared.ctx;
-      promises = prepared.promises;
-      break;
-    }
-    case 'node':
-    case 'electron-main':
-      ctx = prepareNodeContext(parent.filePath, globals);
-      break;
-    case 'electron-renderer': {
-      let browser = prepareBrowserContext(parent.filePath, globals);
-      ctx = {
-        ...browser.ctx,
-        ...prepareNodeContext(parent.filePath, globals),
-      };
-      promises = browser.promises;
-      break;
+  if (entryAsset.env.isBrowser()) {
+    let prepared = prepareBrowserContext(parent.filePath, globals);
+    ctx = prepared.ctx;
+    promises = prepared.promises;
+  }
+
+  if (entryAsset.env.isNode()) {
+    let prepared = prepareNodeContext(parent.filePath, globals);
+    if (ctx) {
+      Object.assign(ctx, prepared);
+    } else {
+      ctx = prepared;
     }
-    default:
-      throw new Error('Unknown target ' + target);
   }
 
+  if (!ctx) {
+    throw new Error(
+      'Unknown context ' + [...entryAsset.env.context].join(', '),
+    );
+  }
+
+  let prepareCode = (code, b) => {
+    if (b.env.outputFormat === 'esmodule' || /\simport\(/.test(code)) {
+      return transformSync(code, {
+        babelrc: false,
+        configFile: false,
+        plugins: [
+          b.env.outputFormat === 'esmodule'
+            ? require('@babel/plugin-transform-modules-commonjs')
+            : null,
+          ({types: t}) => ({
+            visitor: {
+              Import(path) {
+                path.replaceWith(t.identifier('__import'));
+              },
+            },
+          }),
+        ].filter(Boolean),
+      }).code;
+    }
+    return code;
+  };
+
+  // $FlowFixMe
+  ctx.__import = specifier => {
+    let promise = Promise.resolve().then(() => {
+      let filePath = path.join(path.dirname(parent.filePath), specifier);
+      let b = nullthrows(
+        bundleGraph.getBundles().find(b => b.filePath === filePath),
+      );
+      return runBundle(bundleGraph, b, globals, opts);
+    });
+
+    if (promises) {
+      promises.push(promise);
+    }
+
+    return promise;
+  };
+
   vm.createContext(ctx);
-  for (let b of bundles) {
-    new vm.Script(await overlayFS.readFile(nullthrows(b.filePath), 'utf8'), {
+  for (let [code, b] of bundles) {
+    code = await prepareCode(code, b);
+    new vm.Script(code, {
       filename: b.name,
     }).runInContext(ctx);
   }
@@ -295,27 +332,38 @@ export async function runBundle(
       lowerCaseAttributeNames: true,
     });
 
+    let bundles = bundleGraph.getBundles();
     let scripts = [];
     postHtml().walk.call(ast, node => {
-      if (node.tag === 'script') {
+      if (
+        node.tag === 'script' &&
+        node.attrs &&
+        node.attrs.src &&
+        node.attrs.type !== 'module'
+      ) {
         let src = url.parse(nullthrows(node.attrs).src);
         if (src.hostname == null) {
-          scripts.push(path.join(distDir, nullthrows(src.pathname)));
+          let p = path.join(distDir, nullthrows(src.pathname));
+          let b = nullthrows(bundles.find(b => b.filePath === p));
+          scripts.push([overlayFS.readFileSync(b.filePath, 'utf8'), b]);
         }
+      } else if (node.tag === 'script' && node.content && !node.attrs?.src) {
+        let content = node.content.join('');
+        let inline = bundles.filter(b => b.isInline && b.type === 'js');
+        scripts.push([content, inline[0]]); // TODO: match by content??
       }
       return node;
     });
 
-    let bundles = bundleGraph.getBundles();
+    return runBundles(bundleGraph, bundle, scripts, globals, opts);
+  } else {
     return runBundles(
       bundleGraph,
       bundle,
-      scripts.map(p => nullthrows(bundles.find(b => b.filePath === p))),
+      [[overlayFS.readFileSync(bundle.filePath, 'utf8'), bundle]],
       globals,
       opts,
     );
-  } else {
-    return runBundles(bundleGraph, bundle, [bundle], globals, opts);
   }
 }
 
diff --git a/packages/core/types/index.js b/packages/core/types/index.js
index 12c3b30c513..a63a543089c 100644
--- a/packages/core/types/index.js
+++ b/packages/core/types/index.js
@@ -57,7 +57,7 @@ export type RawParcelConfig = {|
   transformers?: {[Glob]: RawParcelConfigPipeline, ...},
   bundler?: PackageName,
   namers?: RawParcelConfigPipeline,
-  runtimes?: {[EnvironmentContext]: RawParcelConfigPipeline, ...},
+  runtimes?: RawParcelConfigPipeline,
   packagers?: {[Glob]: PackageName, ...},
   optimizers?: {[Glob]: RawParcelConfigPipeline, ...},
   reporters?: RawParcelConfigPipeline,
@@ -109,7 +109,9 @@ export type EnvironmentContext =
   | 'service-worker'
   | 'node'
   | 'electron-main'
-  | 'electron-renderer';
+  | 'electron-renderer'
+  | 'script'
+  | 'module';
 
 /** The JS module format for the bundle output */
 export type OutputFormat = 'esmodule' | 'commonjs' | 'global';
@@ -120,7 +122,7 @@ export type OutputFormat = 'esmodule' | 'commonjs' | 'global';
  * See Environment and Target.
  */
 export type PackageTargetDescriptor = {|
-  +context?: EnvironmentContext,
+  +context?: EnvironmentContext | Array<EnvironmentContext>,
   +engines?: Engines,
   +includeNodeModules?:
     | boolean
@@ -149,7 +151,7 @@ export type TargetDescriptor = {|
  * This is used when creating an Environment (see that).
  */
 export type EnvironmentOpts = {|
-  +context?: EnvironmentContext,
+  +context?: EnvironmentContext | Iterable<EnvironmentContext>,
   +engines?: Engines,
   +includeNodeModules?:
     | boolean
@@ -159,7 +161,8 @@ export type EnvironmentOpts = {|
   +isLibrary?: boolean,
   +minify?: boolean,
   +scopeHoist?: boolean,
-  +sourceMap?: ?TargetSourceMapOptions
+  +sourceMap?: ?TargetSourceMapOptions,
+  +loc?: ?SourceLocation
 |};
 
 /**
@@ -179,11 +182,17 @@ export type VersionMap = {
   ...,
 };
 
+export type EnvironmentFeature =
+  | 'esmodules'
+  | 'dynamic-import'
+  | 'worker-type'
+  | 'service-worker-type';
+
 /**
  * Defines the environment in for the output bundle
  */
 export interface Environment {
-  +context: EnvironmentContext;
+  +context: Set<EnvironmentContext>;
   +engines: Engines;
   /** Whether to include all/none packages \
    *  (<code>true / false</code>), an array of package names to include, or an object \
@@ -201,6 +210,7 @@ export interface Environment {
   /** Whether scope hoisting is enabled. */
   +scopeHoist: boolean;
   +sourceMap: ?TargetSourceMapOptions;
+  +loc: ?SourceLocation;
 
   /** Whether <code>context</code> specifies a browser context. */
   isBrowser(): boolean;
@@ -213,6 +223,7 @@ export interface Environment {
   /** Whether <code>context</code> specifies an isolated context (can't access other loaded ancestor bundles). */
   isIsolated(): boolean;
   matchesEngines(minVersions: VersionMap): boolean;
+  supports(feature: EnvironmentFeature): boolean;
 }
 
 /**
@@ -1129,6 +1140,7 @@ export type RuntimeAsset = {|
   +code: string,
   +dependency?: Dependency,
   +isEntry?: boolean,
+  +env?: EnvironmentOpts,
 |};
 
 /**
diff --git a/packages/core/utils/src/index.js b/packages/core/utils/src/index.js
index 45806d41774..81e7c10fb95 100644
--- a/packages/core/utils/src/index.js
+++ b/packages/core/utils/src/index.js
@@ -76,3 +76,4 @@ export {
   loadSourceMapUrl,
   loadSourceMap,
 } from './sourcemap';
+export {setIntersects, isSetEqual, isSubset} from './set';
diff --git a/packages/core/utils/src/set.js b/packages/core/utils/src/set.js
new file mode 100644
index 00000000000..081d1f5d6f1
--- /dev/null
+++ b/packages/core/utils/src/set.js
@@ -0,0 +1,50 @@
+// @flow
+
+export function setIntersects<T>(a: Set<T>, b: Set<T>): boolean {
+  for (let item of a) {
+    if (b.has(item)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+export function isSetEqual<T>(a: Set<T>, b: Set<T>): boolean {
+  if (a.size !== b.size) {
+    return false;
+  }
+
+  for (let item of a) {
+    if (!b.has(item)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/**
+ * Returns true if either set is a subset of the other.
+ */
+export function isSubset<T>(a: Set<T>, b: Set<T>): boolean {
+  let res = true;
+  for (let item of b) {
+    if (!a.has(item)) {
+      res = false;
+      break;
+    }
+  }
+
+  if (!res) {
+    res = true;
+    for (let item of a) {
+      if (!b.has(item)) {
+        res = false;
+        break;
+      }
+    }
+  }
+
+  return res;
+}
diff --git a/packages/packagers/js/src/JSPackager.js b/packages/packagers/js/src/JSPackager.js
index 476f5ffcfdf..4b6344e9a98 100644
--- a/packages/packagers/js/src/JSPackager.js
+++ b/packages/packagers/js/src/JSPackager.js
@@ -49,6 +49,21 @@ export default (new Packager({
     config,
     options,
   }) {
+    // If this is a non-module script, and there is only one asset with no dependencies,
+    // then we don't need to package at all and can pass through the original code un-wrapped.
+    if (bundle.env.context.has('script')) {
+      let entries = bundle.getEntryAssets();
+      if (
+        entries.length === 1 &&
+        bundleGraph.getDependencies(entries[0]).length === 0
+      ) {
+        return {
+          contents: await entries[0].getCode(),
+          map: await entries[0].getMap(),
+        };
+      }
+    }
+
     function replaceReferences({contents, map}) {
       return replaceInlineReferences({
         bundle,
@@ -254,9 +269,35 @@ function getPrefix(
     }
   }
 
+  let globalVars = '';
+  let topLevelVars = mainEntry?.meta.topLevelVars;
+  if (
+    topLevelVars != null &&
+    typeof topLevelVars === 'object' &&
+    !Array.isArray(topLevelVars)
+  ) {
+    let vars = {};
+    for (let key in topLevelVars) {
+      let type = topLevelVars[key];
+      invariant(typeof type === 'string');
+      if (vars[type]) {
+        vars[type] += `, ${key}`;
+      } else {
+        vars[type] = `${type} ${key}`;
+      }
+    }
+
+    for (let type in vars) {
+      globalVars += `${vars[type]};\n`;
+    }
+  }
+
   return (
     // If the entry asset included a hashbang, repeat it at the top of the bundle
-    (interpreter != null ? `#!${interpreter}\n` : '') + importScripts + PRELUDE
+    (interpreter != null ? `#!${interpreter}\n` : '') +
+    globalVars +
+    importScripts +
+    PRELUDE
   );
 }
 
diff --git a/packages/runtimes/js/src/JSRuntime.js b/packages/runtimes/js/src/JSRuntime.js
index c2388016b19..f1ef2f8073a 100644
--- a/packages/runtimes/js/src/JSRuntime.js
+++ b/packages/runtimes/js/src/JSRuntime.js
@@ -10,20 +10,10 @@ import type {
 } from '@parcel/types';
 
 import {Runtime} from '@parcel/plugin';
-import {flatMap, relativeBundlePath} from '@parcel/utils';
+import {flatMap, relativeBundlePath, isSubset} from '@parcel/utils';
 import path from 'path';
 import nullthrows from 'nullthrows';
 
-// List of browsers that support dynamic import natively
-// https://caniuse.com/#feat=es6-module-dynamic-import
-const DYNAMIC_IMPORT_BROWSERS = {
-  edge: '76',
-  firefox: '67',
-  chrome: '63',
-  safari: '11.1',
-  opera: '50',
-};
-
 // Used for as="" in preload/prefetch
 const TYPE_TO_RESOURCE_PRIORITY = {
   css: 'style',
@@ -110,6 +100,7 @@ export default (new Runtime({
             './' + path.relative(options.projectRoot, resolved.value.filePath),
           )}))`,
           dependency,
+          env: createEnvironment(dependency.env),
         });
       } else {
         let loaderRuntime = getLoaderRuntime({
@@ -137,6 +128,7 @@ export default (new Runtime({
           filePath: path.join(__dirname, `/bundles/${referencedBundle.id}.js`),
           code: `module.exports = ${JSON.stringify(dependency.id)};`,
           dependency,
+          env: createEnvironment(dependency.env),
         });
         continue;
       }
@@ -153,6 +145,7 @@ export default (new Runtime({
             dependency.moduleSpecifier,
           )}`,
           dependency,
+          env: createEnvironment(dependency.env),
         });
         continue;
       }
@@ -177,6 +170,7 @@ export default (new Runtime({
             bundle,
             mainBundle,
           )})`,
+          env: createEnvironment(dependency.env),
         });
         continue;
       }
@@ -194,6 +188,7 @@ export default (new Runtime({
         filePath: __filename,
         code: getRegisterCode(bundle, bundleGraph),
         isEntry: true,
+        env: createEnvironment(bundle.env),
       });
     }
 
@@ -239,12 +234,7 @@ function getLoaderRuntime({
   }
 
   // Determine if we need to add a dynamic import() polyfill, or if all target browsers support it natively.
-  let needsDynamicImportPolyfill = false;
-  if (bundle.env.isBrowser() && bundle.env.outputFormat === 'esmodule') {
-    needsDynamicImportPolyfill = !bundle.env.matchesEngines(
-      DYNAMIC_IMPORT_BROWSERS,
-    );
-  }
+  let needsDynamicImportPolyfill = !bundle.env.supports('dynamic-import');
 
   let loaderModules = externalBundles
     .map(to => {
@@ -263,7 +253,9 @@ function getLoaderRuntime({
 
         loader = nullthrows(
           loaders.IMPORT_POLYFILL,
-          `No import() polyfill available for context '${bundle.env.context}'`,
+          `No import() polyfill available for context '${[
+            ...bundle.env.context,
+          ].join(', ')}'`,
         );
       } else if (to.type === 'js' && to.env.outputFormat === 'commonjs') {
         return `Promise.resolve(require("./" + ${relativePathExpr}))`;
@@ -275,7 +267,7 @@ function getLoaderRuntime({
     })
     .filter(Boolean);
 
-  if (bundle.env.context === 'browser') {
+  if (bundle.env.isBrowser() && !bundle.env.isWorker()) {
     loaderModules.push(
       ...flatMap(
         // TODO: Allow css to preload resources as well
@@ -307,20 +299,22 @@ function getLoaderRuntime({
   }
 
   let loaderCode = loaderModules.join(', ');
+  let targetFormat =
+    externalBundles[externalBundles.length - 1].env.outputFormat;
   if (
     loaderModules.length > 1 &&
-    (bundle.env.outputFormat === 'global' ||
+    (externalBundles.some(b => b.env.outputFormat === 'global') ||
       !externalBundles.every(b => b.type === 'js'))
   ) {
     loaderCode = `Promise.all([${loaderCode}])`;
-    if (bundle.env.outputFormat !== 'global') {
+    if (targetFormat !== 'global') {
       loaderCode += `.then(r => r[r.length - 1])`;
     }
   } else {
     loaderCode = `(${loaderCode})`;
   }
 
-  if (bundle.env.outputFormat === 'global') {
+  if (targetFormat === 'global') {
     loaderCode += `.then(() => module.bundle.root('${bundleGraph.getAssetPublicId(
       bundleGraph.getAssetById(bundleGroup.entryAssetId),
     )}')${
@@ -334,6 +328,7 @@ function getLoaderRuntime({
     filePath: __filename,
     code: `module.exports = ${loaderCode};`,
     dependency,
+    env: createEnvironment(dependency.env),
   };
 }
 
@@ -414,7 +409,8 @@ function isNewContext(
     parents.length === 0 ||
     parents.some(
       parent =>
-        parent.env.context !== bundle.env.context || parent.type !== 'js',
+        !isSubset(parent.env.context, bundle.env.context) ||
+        parent.type !== 'js',
     )
   );
 }
@@ -430,6 +426,7 @@ function getURLRuntime(
       filePath: __filename,
       code: `module.exports = require('./get-worker-url')(${relativePathExpr});`,
       dependency,
+      env: createEnvironment(dependency.env),
     };
   }
 
@@ -437,6 +434,17 @@ function getURLRuntime(
     filePath: __filename,
     code: `module.exports = require('./bundle-url').getBundleURL() + ${relativePathExpr}`,
     dependency,
+    env: createEnvironment(dependency.env),
+  };
+}
+
+function createEnvironment(env: Environment) {
+  // Ensure that the context does not contain "script" or dependencies won't be allowed.
+  let context = new Set(env.context);
+  context.delete('script');
+  context.add('module');
+  return {
+    context,
   };
 }
 
@@ -477,5 +485,10 @@ function getRelativePathExpr(from: NamedBundle, to: NamedBundle): string {
 
 function shouldUseRuntimeManifest(bundle: NamedBundle): boolean {
   let env = bundle.env;
-  return !env.isLibrary && env.outputFormat === 'global' && env.isBrowser();
+  return (
+    !env.isLibrary &&
+    env.outputFormat === 'global' &&
+    env.isBrowser() &&
+    !bundle.isInline
+  );
 }
diff --git a/packages/shared/babel-ast-utils/src/index.js b/packages/shared/babel-ast-utils/src/index.js
index 36795bf7d18..dd1a310fdf0 100644
--- a/packages/shared/babel-ast-utils/src/index.js
+++ b/packages/shared/babel-ast-utils/src/index.js
@@ -36,6 +36,8 @@ export async function parse({
         strictMode: false,
         sourceType: 'module',
         plugins: ['exportDefaultFrom', 'exportNamespaceFrom', 'dynamicImport'],
+        // $FlowFixMe
+        startLine: asset.meta.loc?.start.line,
       }),
     };
   } catch (e) {
diff --git a/packages/shared/scope-hoisting/src/generate.js b/packages/shared/scope-hoisting/src/generate.js
index b3f65b623b0..7fd9c2f75cf 100644
--- a/packages/shared/scope-hoisting/src/generate.js
+++ b/packages/shared/scope-hoisting/src/generate.js
@@ -90,6 +90,27 @@ export function generate({
       : [WRAPPER_TEMPLATE({STATEMENTS: statements})];
   }
 
+  let topLevelVars = mainEntry?.meta.topLevelVars;
+  if (
+    topLevelVars &&
+    typeof topLevelVars === 'object' &&
+    !Array.isArray(topLevelVars)
+  ) {
+    let vars = {};
+    for (let key in topLevelVars) {
+      let type = topLevelVars[key];
+      invariant(typeof type === 'string');
+      let decl = t.variableDeclarator(t.identifier(key));
+      if (vars[type]) {
+        vars[type].declarations.push(decl);
+      } else {
+        // $FlowFixMe
+        vars[type] = t.variableDeclaration(type, [decl]);
+        statements.unshift(vars[type]);
+      }
+    }
+  }
+
   ast = t.file(
     t.program(
       statements,
diff --git a/packages/shared/scope-hoisting/src/utils.js b/packages/shared/scope-hoisting/src/utils.js
index e01f6f5ead6..9cbe631de8d 100644
--- a/packages/shared/scope-hoisting/src/utils.js
+++ b/packages/shared/scope-hoisting/src/utils.js
@@ -25,6 +25,7 @@ import {isVariableDeclarator, isVariableDeclaration} from '@babel/types';
 import invariant from 'assert';
 import nullthrows from 'nullthrows';
 import path from 'path';
+import {isSubset} from '@parcel/utils';
 
 export function getName(
   asset: Asset | MutableAsset,
@@ -125,7 +126,7 @@ export function hasAsyncDescendant(
       return;
     }
 
-    if (b.env.context !== bundle.env.context || b.type !== 'js') {
+    if (!isSubset(b.env.context, bundle.env.context) || b.type !== 'js') {
       actions.skipChildren();
       return;
     }
diff --git a/packages/transformers/babel/src/babel7.js b/packages/transformers/babel/src/babel7.js
index dfa0c2298f1..1f9019b5cd8 100644
--- a/packages/transformers/babel/src/babel7.js
+++ b/packages/transformers/babel/src/babel7.js
@@ -42,6 +42,8 @@ export default async function babel7(
       strictMode: false,
       sourceType: 'module',
       plugins: ['dynamicImport'],
+      // $FlowFixMe
+      startLine: asset.meta.loc?.start.line,
     },
     caller: {
       name: 'parcel',
diff --git a/packages/transformers/html/package.json b/packages/transformers/html/package.json
index 3dcf18d3bbc..89339fc2cdf 100644
--- a/packages/transformers/html/package.json
+++ b/packages/transformers/html/package.json
@@ -21,10 +21,10 @@
   },
   "dependencies": {
     "@parcel/plugin": "2.0.0-beta.1",
+    "@parcel/posthtml-parser": "^0.6.0",
     "@parcel/utils": "2.0.0-beta.1",
     "nullthrows": "^1.1.1",
     "posthtml": "^0.11.3",
-    "posthtml-parser": "^0.4.1",
     "posthtml-render": "^1.1.5",
     "semver": "^5.4.1"
   }
diff --git a/packages/transformers/html/src/HTMLTransformer.js b/packages/transformers/html/src/HTMLTransformer.js
index 13d3d9dbe43..98c634f9643 100644
--- a/packages/transformers/html/src/HTMLTransformer.js
+++ b/packages/transformers/html/src/HTMLTransformer.js
@@ -1,7 +1,7 @@
 // @flow
 
 import {Transformer} from '@parcel/plugin';
-import parse from 'posthtml-parser';
+import parse from '@parcel/posthtml-parser';
 import nullthrows from 'nullthrows';
 import render from 'posthtml-render';
 import semver from 'semver';
diff --git a/packages/transformers/html/src/dependencies.js b/packages/transformers/html/src/dependencies.js
index ed69312d62f..17e883f0a30 100644
--- a/packages/transformers/html/src/dependencies.js
+++ b/packages/transformers/html/src/dependencies.js
@@ -1,6 +1,7 @@
 // @flow
 
-import type {AST, Environment, MutableAsset} from '@parcel/types';
+import type {AST, MutableAsset} from '@parcel/types';
+import type {PostHTMLNode} from 'posthtml';
 import PostHTML from 'posthtml';
 
 // A list of all attributes that may produce a dependency
@@ -81,18 +82,6 @@ const OPTIONS = {
       };
     }
   },
-  script(attrs, env: Environment) {
-    return {
-      // Keep in the same bundle group as the HTML.
-      isAsync: false,
-      isEntry: false,
-      isIsolated: true,
-      env: {
-        outputFormat:
-          attrs.type === 'module' && env.scopeHoist ? 'esmodule' : undefined,
-      },
-    };
-  },
 };
 
 function collectSrcSetDependencies(asset, srcset, opts) {
@@ -120,12 +109,15 @@ function getAttrDepHandler(attr) {
 
 export default function collectDependencies(asset: MutableAsset, ast: AST) {
   let isDirty = false;
+  let seen = new Set();
   PostHTML().walk.call(ast.program, node => {
     let {tag, attrs} = node;
-    if (!attrs) {
+    if (!attrs || seen.has(node)) {
       return node;
     }
 
+    seen.add(node);
+
     if (tag === 'meta') {
       if (
         !Object.keys(attrs).some(attr => {
@@ -154,6 +146,70 @@ export default function collectDependencies(asset: MutableAsset, ast: AST) {
       return node;
     }
 
+    if (tag === 'script' && attrs.src) {
+      let context = new Set(asset.env.context);
+      context.delete('module');
+      context.delete('script');
+      context.add(attrs.type === 'module' ? 'module' : 'script');
+
+      let loc = node.loc
+        ? {
+            filePath: asset.filePath,
+            start: node.loc.start,
+            end: node.loc.end,
+          }
+        : undefined;
+
+      let outputFormat = 'global';
+      if (attrs.type === 'module' && asset.env.scopeHoist) {
+        outputFormat = 'esmodule';
+      } else {
+        delete attrs.type;
+      }
+
+      // If this is a <script type="module">, and not all of the browser targets support ESM natively,
+      // add a copy of the script tag with a nomodule attribute.
+      let copy: ?PostHTMLNode;
+      if (
+        outputFormat === 'esmodule' &&
+        asset.env.engines.browsers &&
+        !asset.env.supports('esmodules')
+      ) {
+        let attrs: {[string]: string, ...} = {...node.attrs};
+        copy = {...node, attrs};
+        delete attrs.type;
+        attrs.nomodule = '';
+        attrs.src = asset.addURLDependency(attrs.src, {
+          // Keep in the same bundle group as the HTML.
+          isAsync: false,
+          isEntry: false,
+          isIsolated: true,
+          env: {
+            context,
+            outputFormat: 'global',
+            loc,
+          },
+        });
+
+        seen.add(copy);
+      }
+
+      attrs.src = asset.addURLDependency(attrs.src, {
+        // Keep in the same bundle group as the HTML.
+        isAsync: false,
+        isEntry: false,
+        isIsolated: true,
+        env: {
+          context,
+          outputFormat,
+          loc,
+        },
+      });
+
+      asset.setAST(ast);
+      return copy ? [node, copy] : node;
+    }
+
     for (let attr in attrs) {
       // Check for virtual paths
       if (tag === 'a' && attrs[attr].lastIndexOf('.') < 1) {
diff --git a/packages/transformers/html/src/inline.js b/packages/transformers/html/src/inline.js
index 067cd404b7c..723f44433e9 100644
--- a/packages/transformers/html/src/inline.js
+++ b/packages/transformers/html/src/inline.js
@@ -27,17 +27,21 @@ export default function extractInlineAssets(
   new PostHTML().walk.call(program, (node: PostHTMLNode) => {
     let parcelKey = md5FromString(`${asset.id}:${key++}`);
     if (node.tag === 'script' || node.tag === 'style') {
-      let value = node.content && node.content.join('').trim();
+      let value = node.content && node.content.join('');
       if (value != null) {
         let type, env;
 
+        let context = new Set(asset.env.context);
+        context.delete('module');
+        context.delete('script');
+
         if (node.tag === 'style') {
           if (node.attrs && node.attrs.type) {
             type = node.attrs.type.split('/')[1];
           } else {
             type = 'css';
           }
-        } else if (node.attrs && node.attrs.type) {
+        } else if (node.attrs && node.attrs.type != null) {
           // Skip JSON
           if (SCRIPT_TYPES[node.attrs.type] === false) {
             return node;
@@ -49,13 +53,33 @@ export default function extractInlineAssets(
             type = node.attrs.type.split('/')[1];
           }
 
-          if (node.attrs.type === 'module' && asset.env.scopeHoist) {
-            env = {
-              outputFormat: 'esmodule',
-            };
+          let outputFormat = 'global';
+          if (node.attrs.type === 'module') {
+            if (
+              asset.env.scopeHoist &&
+              (asset.env.engines.browsers == null ||
+                asset.env.supports('esmodules'))
+            ) {
+              outputFormat = 'esmodule';
+            } else {
+              delete node.attrs.type;
+            }
+
+            context.add('module');
+          } else {
+            context.add('script');
           }
+
+          env = {
+            context,
+            outputFormat,
+          };
         } else {
           type = 'js';
+          context.add('script');
+          env = {
+            context,
+          };
         }
 
         if (!node.attrs) {
@@ -69,12 +93,7 @@ export default function extractInlineAssets(
         }
 
         // Inform packager to remove type, since CSS and JS are the defaults.
-        // Unless it's application/ld+json
-        if (
-          node.attrs &&
-          (node.tag === 'style' ||
-            (node.attrs.type && SCRIPT_TYPES[node.attrs.type] === 'js'))
-        ) {
+        if (node.attrs?.type && node.tag === 'style') {
           delete node.attrs.type;
         }
 
@@ -95,6 +114,7 @@ export default function extractInlineAssets(
           meta: {
             type: 'tag',
             node,
+            loc: node.loc,
           },
         });
       }
diff --git a/packages/transformers/js/src/JSTransformer.js b/packages/transformers/js/src/JSTransformer.js
index 1a83e534b69..311c2bc1616 100644
--- a/packages/transformers/js/src/JSTransformer.js
+++ b/packages/transformers/js/src/JSTransformer.js
@@ -10,6 +10,7 @@ import collectDependencies from './visitors/dependencies';
 import processVisitor from './visitors/process';
 import fsVisitor from './visitors/fs';
 import insertGlobals from './visitors/globals';
+import {assignScriptGlobals} from './visitors/script-globals';
 import traverse from '@babel/traverse';
 import {ancestor as walkAncestor} from '@parcel/babylon-walk';
 import * as babelCore from '@babel/core';
@@ -134,8 +135,9 @@ export default (new Transformer({
 
     // Inline process/environment variables
     if (
-      (!asset.env.isNode() && (code == null || ENV_RE.test(code))) ||
-      (asset.env.isBrowser() && (code == null || BROWSER_RE.test(code)))
+      !asset.env.context.has('script') &&
+      ((!asset.env.isNode() && (code == null || ENV_RE.test(code))) ||
+        (asset.env.isBrowser() && (code == null || BROWSER_RE.test(code))))
     ) {
       walkAncestor(ast.program, processVisitor, {
         asset,
@@ -148,7 +150,7 @@ export default (new Transformer({
     }
 
     let isASTDirty;
-    if (!asset.env.isNode()) {
+    if (!asset.env.isNode() && !asset.env.context.has('script')) {
       // Inline fs calls, run before globals to also collect Buffer
       if (code == null || FS_RE.test(code)) {
         if (!ignoreFS) {
@@ -184,6 +186,18 @@ export default (new Transformer({
       walkAncestor(ast.program, collectDependencies, {asset, ast, options});
     }
 
+    // If this is a non-module script, and this asset has dependencies, then we need to
+    // create assignments for all top-level variables to the global scope. If there are
+    // no dependencies, we can skip this and scope hoisting completely and just pass through
+    // the original source code as no bundling is needed.
+    if (asset.env.context.has('script')) {
+      if (asset.getDependencies().length > 0) {
+        assignScriptGlobals(asset, ast, options);
+      } else {
+        return [asset];
+      }
+    }
+
     // If there's a hashbang, remove it and store it on the asset meta.
     // During packaging, if this is the entry asset, it will be prepended to the
     // packaged output.
diff --git a/packages/transformers/js/src/visitors/dependencies.js b/packages/transformers/js/src/visitors/dependencies.js
index c4df2fcc5ea..ab964c76d73 100644
--- a/packages/transformers/js/src/visitors/dependencies.js
+++ b/packages/transformers/js/src/visitors/dependencies.js
@@ -4,7 +4,6 @@ import type {
   AST,
   DependencyOptions,
   JSONObject,
-  Meta,
   MutableAsset,
   PluginOptions,
 } from '@parcel/types';
@@ -22,18 +21,22 @@ import {
   isFunction,
 } from '@babel/types';
 import {isURL, md5FromString, createDependencyLocation} from '@parcel/utils';
+import ThrowableDiagnostic from '@parcel/diagnostic';
 import {isInFalsyBranch, hasBinding, morph} from './utils';
+import {convertBabelLoc} from '@parcel/babel-ast-utils';
 
 const serviceWorkerPattern = ['navigator', 'serviceWorker', 'register'];
 
 export default ({
   ImportDeclaration(node, {asset}) {
     asset.meta.isES6Module = true;
+    checkModule(asset, node);
     addDependency(asset, node.source);
   },
 
   ExportNamedDeclaration(node, {asset}) {
     asset.meta.isES6Module = true;
+    checkModule(asset, node);
     if (node.source) {
       addDependency(asset, node.source);
     }
@@ -41,11 +44,13 @@ export default ({
 
   ExportAllDeclaration(node, {asset}) {
     asset.meta.isES6Module = true;
+    checkModule(asset, node);
     addDependency(asset, node.source);
   },
 
   ExportDefaultDeclaration(node, {asset}) {
     asset.meta.isES6Module = true;
+    checkModule(asset, node);
   },
 
   CallExpression: {
@@ -64,6 +69,7 @@ export default ({
         let isOptional =
           ancestors.some(a => types.isTryStatement(a)) || undefined;
         let isAsync = isRequireAsync(ancestors, node, asset, ast);
+        checkModule(asset, node);
         addDependency(asset, args[0], {isOptional, isAsync});
         return;
       }
@@ -79,6 +85,7 @@ export default ({
       if (isRequireResolve) {
         let isOptional =
           ancestors.some(a => types.isTryStatement(a)) || undefined;
+        checkModule(asset, node);
         addDependency(asset, args[0], {isOptional});
         return;
       }
@@ -112,7 +119,38 @@ export default ({
           args.splice(1, 1);
         }
 
-        addDependency(asset, args[0], {isAsync: true, meta});
+        let context = new Set(asset.env.context);
+        context.delete('script');
+        context.add('module');
+
+        // If no browser engines are defined, or all browsers support dynamic import natively,
+        // we can output native ESM if scope hoisting is enabled.
+        let outputFormat = asset.env.outputFormat;
+        if (
+          asset.env.context.has('script') &&
+          asset.env.scopeHoist &&
+          asset.env.isBrowser() &&
+          (!asset.env.engines.browsers || asset.env.supports('dynamic-import'))
+        ) {
+          outputFormat = 'esmodule';
+        }
+
+        let loc = convertBabelLoc(node.loc);
+        addDependency(asset, args[0], {
+          isAsync: true,
+          meta,
+          env: {
+            context,
+            outputFormat,
+            loc: loc
+              ? {
+                  filePath: asset.filePath,
+                  start: loc.start,
+                  end: loc.end,
+                }
+              : undefined,
+          },
+        });
 
         node.callee = types.identifier('require');
         asset.setAST(ast);
@@ -134,11 +172,45 @@ export default ({
         !isInFalsyBranch(ancestors);
 
       if (isRegisterServiceWorker) {
-        // Treat service workers as an entry point so filenames remain consistent across builds.
-        // https://developers.google.com/web/fundamentals/primers/service-workers/lifecycle#avoid_changing_the_url_of_your_service_worker_script
+        let isModule = false;
+        if (types.isObjectExpression(args[1])) {
+          let propIndex = args[1].properties.findIndex(v =>
+            types.isIdentifier(v.key, {name: 'type'}),
+          );
+          let prop = propIndex >= 0 ? args[1].properties[propIndex] : null;
+          if (prop && types.isStringLiteral(prop.value)) {
+            isModule = prop.value.value === 'module';
+          }
+
+          // No browsers currently implement the type: module option.
+          // Delete it since we'll be transpiling modules.
+          if (isModule) {
+            // Remove the whole options argument if `type` is the only option.
+            // Otherwise, just remove the type option.
+            if (args[1].properties.length === 1) {
+              args.splice(1, 1);
+            } else {
+              args[1].properties.splice(propIndex, 1);
+            }
+          }
+        }
+
+        let loc = convertBabelLoc(node.loc);
         addURLDependency(asset, ast, args[0], {
+          // Treat service workers as an entry point so filenames remain consistent across builds.
+          // https://developers.google.com/web/fundamentals/primers/service-workers/lifecycle#avoid_changing_the_url_of_your_service_worker_script
           isEntry: true,
-          env: {context: 'service-worker'},
+          env: {
+            context: ['service-worker', isModule ? 'module' : 'script'],
+            outputFormat: 'global',
+            loc: loc
+              ? {
+                  filePath: asset.filePath,
+                  start: loc.start,
+                  end: loc.end,
+                }
+              : undefined,
+          },
         });
         return;
       }
@@ -171,19 +243,49 @@ export default ({
 
       if (isWebWorker) {
         let isModule = false;
+        let outputFormat = 'global';
         if (types.isObjectExpression(args[1])) {
-          let prop = args[1].properties.find(v =>
+          let propIndex = args[1].properties.findIndex(v =>
             types.isIdentifier(v.key, {name: 'type'}),
           );
-          if (prop && types.isStringLiteral(prop.value))
+          let prop = propIndex >= 0 ? args[1].properties[propIndex] : null;
+          if (prop && types.isStringLiteral(prop.value)) {
             isModule = prop.value.value === 'module';
+          }
+
+          if (isModule) {
+            // If scope hoisting is enabled, we can output native ESM.
+            // If no browser engines are defined, pass through as ESM.
+            // If the engines defined don't support ESM, transpile to a classic script.
+            if (
+              asset.env.scopeHoist &&
+              (!asset.env.engines.browsers || asset.env.supports('worker-type'))
+            ) {
+              outputFormat = 'esmodule';
+            } else {
+              // Remove the whole options argument if `type` is the only option.
+              // Otherwise, just remove the type option.
+              if (args[1].properties.length === 1) {
+                args.splice(1, 1);
+              } else {
+                args[1].properties.splice(propIndex, 1);
+              }
+            }
+          }
         }
 
+        let loc = convertBabelLoc(node.loc);
         addURLDependency(asset, ast, args[0], {
           env: {
-            context: 'web-worker',
-            outputFormat:
-              isModule && asset.env.scopeHoist ? 'esmodule' : undefined,
+            context: ['web-worker', isModule ? 'module' : 'script'],
+            outputFormat,
+            loc: loc
+              ? {
+                  filePath: asset.filePath,
+                  start: loc.start,
+                  end: loc.end,
+                }
+              : undefined,
           },
           meta: {
             webworker: true,
@@ -309,22 +411,13 @@ function getFunctionParent(ancestors) {
   }
 }
 
-function addDependency(
-  asset,
-  node,
-  opts: ?{|isAsync?: boolean, isOptional?: boolean, meta?: ?Meta|},
-) {
+function addDependency(asset, node, opts: ?$Shape<DependencyOptions>) {
   let dependencyOptions: DependencyOptions = {
+    ...opts,
     moduleSpecifier: node.value,
     loc: node.loc && createDependencyLocation(node.loc.start, node.value, 0, 1),
-    isAsync: opts ? opts.isAsync : false,
-    isOptional: opts ? opts.isOptional : false,
   };
 
-  if (opts?.meta != null) {
-    dependencyOptions = {...dependencyOptions, meta: opts.meta};
-  }
-
   asset.addDependency(dependencyOptions);
 }
 
@@ -371,3 +464,65 @@ function objectExpressionNodeToJSONObject(
 
   return object;
 }
+
+const messages = {
+  browser:
+    'Browser scripts cannot have imports or exports. Use a <script type="module"> instead.',
+  'web-worker':
+    'Web workers cannot have imports or exports. Use the `type: "module"` option instead.',
+  'service-worker':
+    'Service workers cannot have imports or exports. Use the `type: "module"` option instead.',
+};
+
+function checkModule(asset, node) {
+  if (asset.env.context.has('script')) {
+    let message;
+    for (let context of asset.env.context) {
+      if (context in messages) {
+        message = messages[(context: string)];
+        break;
+      }
+    }
+
+    if (!message) {
+      return;
+    }
+
+    let loc = convertBabelLoc(node.loc);
+    let diagnostic = [
+      {
+        message,
+        filePath: asset.filePath,
+        codeFrame: loc
+          ? {
+              codeHighlights: [
+                {
+                  start: loc.start,
+                  end: loc.end,
+                },
+              ],
+            }
+          : undefined,
+      },
+    ];
+
+    if (asset.env.loc) {
+      diagnostic.push({
+        message: 'The environment was originally created here:',
+        filePath: asset.env.loc.filePath,
+        codeFrame: {
+          codeHighlights: [
+            {
+              start: asset.env.loc.start,
+              end: asset.env.loc.end,
+            },
+          ],
+        },
+      });
+    }
+
+    throw new ThrowableDiagnostic({
+      diagnostic,
+    });
+  }
+}
diff --git a/packages/transformers/js/src/visitors/script-globals.js b/packages/transformers/js/src/visitors/script-globals.js
new file mode 100644
index 00000000000..ff5c314ca8f
--- /dev/null
+++ b/packages/transformers/js/src/visitors/script-globals.js
@@ -0,0 +1,146 @@
+// @flow
+
+import type {AST, MutableAsset, PluginOptions} from '@parcel/types';
+
+import * as types from '@babel/types';
+import {
+  isFunctionDeclaration,
+  isVariableDeclaration,
+  isClassDeclaration,
+  isProgram,
+  isDirective,
+} from '@babel/types';
+import {traverse} from '@parcel/babylon-walk';
+import invariant from 'assert';
+import nullthrows from 'nullthrows';
+
+let scriptGlobalsVisitor = {
+  Function(path) {
+    path.skip();
+  },
+  Block: {
+    enter(path, context) {
+      if (!isProgram(path.node)) {
+        context.isInBlock = true;
+      }
+
+      context.blockStack.push([]);
+    },
+    exit(path, context) {
+      context.isInBlock = false;
+
+      let functionAssignments = context.blockStack.pop();
+      if (functionAssignments.length > 0) {
+        // $FlowFixMe
+        path.node.body.unshift(...functionAssignments);
+        context.asset.setAST(context.ast);
+      }
+    },
+  },
+  Directive(path, context) {
+    if (isDirective(path.node) && path.node.value.value === 'use strict') {
+      context.isStrictMode = true;
+    }
+  },
+  VariableDeclaration(path, {asset, ast, isInBlock}) {
+    let node = path.node;
+    invariant(isVariableDeclaration(node));
+
+    if (isInBlock && node.kind !== 'var') {
+      return;
+    }
+
+    let ids = types.getBindingIdentifiers(node);
+    for (let id in ids) {
+      // $FlowFixMe
+      asset.meta.topLevelVars[id] = node.kind;
+    }
+
+    path.replaceWith(
+      types.expressionStatement(
+        types.sequenceExpression(
+          node.declarations
+            .filter(decl => decl.init)
+            .map(decl =>
+              types.assignmentExpression('=', decl.id, nullthrows(decl.init)),
+            ),
+        ),
+      ),
+    );
+
+    asset.setAST(ast);
+  },
+  FunctionDeclaration(path, {asset, isInBlock, isStrictMode, blockStack}) {
+    let node = path.node;
+    invariant(isFunctionDeclaration(node));
+
+    // In strict mode, function declarations inside blocks are not hoisted to the global scope.
+    if (isInBlock && isStrictMode) {
+      return;
+    }
+
+    let id = node.id;
+    if (!id) {
+      return;
+    }
+
+    let name = id.name;
+    id.name = types.toIdentifier('$' + asset.id) + '$var$' + name;
+    // $FlowFixMe
+    asset.meta.topLevelVars[name] = 'var';
+
+    let assignment = types.expressionStatement(
+      types.assignmentExpression(
+        '=',
+        types.identifier(name),
+        types.identifier(id.name),
+      ),
+    );
+
+    // Follow Annex B.3.3 rules. Function declarations should be hoisted to the top
+    // of the nearest block, or the program if not inside a block. Safari does not
+    // currently implement this rule for globals, but it would be hard to replicate this.
+    // https://tc39.es/ecma262/#sec-block-level-function-declarations-web-legacy-compatibility-semantics
+    blockStack[blockStack.length - 1].push(assignment);
+  },
+  ClassDeclaration(path, {asset, ast, isInBlock}) {
+    let node = path.node;
+    invariant(isClassDeclaration(node));
+    if (isInBlock || !node.id) {
+      return;
+    }
+
+    let name = node.id.name;
+
+    // $FlowFixMe
+    asset.meta.topLevelVars[name] = 'let';
+
+    path.replaceWith(
+      types.expressionStatement(
+        types.assignmentExpression(
+          '=',
+          types.identifier(name),
+          types.toExpression(node),
+        ),
+      ),
+    );
+
+    asset.setAST(ast);
+  },
+};
+
+export function assignScriptGlobals(
+  asset: MutableAsset,
+  ast: AST,
+  options: PluginOptions,
+) {
+  asset.meta.topLevelVars = {};
+  traverse(ast.program, scriptGlobalsVisitor, {
+    asset,
+    ast,
+    options,
+    isStrictMode: false,
+    isInBlock: false,
+    blockStack: [],
+  });
+}
diff --git a/packages/transformers/posthtml/package.json b/packages/transformers/posthtml/package.json
index 9743b041cb2..c500bfecb1b 100644
--- a/packages/transformers/posthtml/package.json
+++ b/packages/transformers/posthtml/package.json
@@ -20,9 +20,9 @@
   },
   "dependencies": {
     "@parcel/plugin": "2.0.0-beta.1",
+    "@parcel/posthtml-parser": "^0.6.0",
     "nullthrows": "^1.1.1",
     "posthtml": "^0.11.3",
-    "posthtml-parser": "^0.4.1",
     "posthtml-render": "^1.1.5",
     "semver": "^5.4.1"
   }
diff --git a/packages/transformers/posthtml/src/PostHTMLTransformer.js b/packages/transformers/posthtml/src/PostHTMLTransformer.js
index caa5f0910a2..cf46352dc27 100644
--- a/packages/transformers/posthtml/src/PostHTMLTransformer.js
+++ b/packages/transformers/posthtml/src/PostHTMLTransformer.js
@@ -4,7 +4,7 @@ import {Transformer} from '@parcel/plugin';
 
 import path from 'path';
 import posthtml from 'posthtml';
-import parse from 'posthtml-parser';
+import parse from '@parcel/posthtml-parser';
 import render from 'posthtml-render';
 import nullthrows from 'nullthrows';
 import semver from 'semver';
diff --git a/packages/utils/babylon-walk/src/traverse.js b/packages/utils/babylon-walk/src/traverse.js
index 28bdaf2b515..b4af25ab77c 100644
--- a/packages/utils/babylon-walk/src/traverse.js
+++ b/packages/utils/babylon-walk/src/traverse.js
@@ -42,6 +42,11 @@ class Path {
     // $FlowFixMe
     this.parent[this.listkey].splice(this.key, 1);
   }
+  insertAfter(...n: Node[]) {
+    invariant(this.listkey && typeof this.key === 'number');
+    // $FlowFixMe
+    this.parent[this.listkey].splice(this.key + 1, 0, ...n);
+  }
 }
 
 export default function traverse<T>(
diff --git a/packages/utils/posthtml-parser/LICENSE b/packages/utils/posthtml-parser/LICENSE
new file mode 100644
index 00000000000..2feff8447f2
--- /dev/null
+++ b/packages/utils/posthtml-parser/LICENSE
@@ -0,0 +1,22 @@
+(The MIT License)
+
+Copyright (c) 2015 Ivan Voischev <voischev.ivan@ya.ru>
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+'Software'), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/packages/utils/posthtml-parser/index.js b/packages/utils/posthtml-parser/index.js
new file mode 100644
index 00000000000..a24ae79fc40
--- /dev/null
+++ b/packages/utils/posthtml-parser/index.js
@@ -0,0 +1,198 @@
+const {Parser} = require('htmlparser2');
+
+/**
+ * @see https://github.com/fb55/htmlparser2/wiki/Parser-options
+ */
+const defaultOptions = {lowerCaseTags: false, lowerCaseAttributeNames: false, decodeEntities: false};
+
+const defaultDirectives = [{name: '!doctype', start: '<', end: '>'}];
+
+/**
+ * Parse html to PostHTMLTree
+ * @param  {String} html
+ * @param  {Object} [options=defaultOptions]
+ * @return {PostHTMLTree}
+ */
+function postHTMLParser(html, options) {
+  const bufArray = [];
+  const results = [];
+
+  bufArray.last = function () {
+    return this[this.length - 1];
+  };
+
+  function isDirective({name}, tag) {
+    if (name instanceof RegExp) {
+      const regex = new RegExp(name.source, 'i');
+
+      return regex.test(tag);
+    }
+
+    if (tag !== name) {
+      return false;
+    }
+
+    return true;
+  }
+
+  function parserDirective(name, data) {
+    const directives = [].concat(defaultDirectives, options.directives || []);
+    const last = bufArray.last();
+
+    for (const directive of directives) {
+      const directiveText = directive.start + data + directive.end;
+
+      name = name.toLowerCase();
+      if (isDirective(directive, name)) {
+        if (!last) {
+          results.push(directiveText);
+          return;
+        }
+
+        if (last.content === undefined) {
+          last.content = [];
+        }
+
+        last.content.push(directiveText);
+      }
+    }
+  }
+
+  function normalizeArributes(attrs) {
+    const result = {};
+    Object.keys(attrs).forEach(key => {
+      const object = {};
+      object[key] = attrs[key].replace(/&quot;/g, '"');
+      Object.assign(result, object);
+    });
+
+    return result;
+  }
+
+  let lastLoc = {
+    line: 1,
+    column: 1
+  };
+
+  let lastIndex = 0;
+  function getLoc(index) {
+    if (index < lastIndex) {
+      throw new Error('Source indices must be monotonic');
+    }
+
+    while (lastIndex < index) {
+      if (html.charCodeAt(lastIndex) === /* \n */ 10) {
+        lastLoc.line++;
+        lastLoc.column = 1;
+      } else {
+        lastLoc.column++;
+      }
+
+      lastIndex++;
+    }
+
+    return {
+      line: lastLoc.line,
+      column: lastLoc.column
+    };
+  }
+
+  const parser = new Parser({
+    onprocessinginstruction: parserDirective,
+    oncomment(data) {
+      const comment = `<!--${data}-->`;
+      const last = bufArray.last();
+
+      if (!last) {
+        results.push(comment);
+        return;
+      }
+
+      if (last.content === undefined) {
+        last.content = [];
+      }
+
+      last.content.push(comment);
+    },
+    onopentag(tag, attrs) {
+      const buf = {
+        tag,
+        loc: {
+          start: getLoc(parser.startIndex),
+          end: null
+        }
+      };
+
+      if (Object.keys(attrs).length > 0) {
+        buf.attrs = normalizeArributes(attrs);
+      }
+
+      bufArray.push(buf);
+    },
+    onclosetag() {
+      const buf = bufArray.pop();
+      buf.loc.end = getLoc(parser.endIndex);
+
+      if (!bufArray.length > 0) {
+        results.push(buf);
+        return;
+      }
+
+      const last = bufArray.last();
+      if (!Array.isArray(last.content)) {
+        last.content = [];
+      }
+
+      last.content.push(buf);
+    },
+    ontext(text) {
+      const last = bufArray.last();
+
+      if (!last) {
+        results.push(text);
+        return;
+      }
+
+      if (last.content && last.content.length > 0 && typeof last.content[last.content.length - 1] === 'string') {
+        last.content[last.content.length - 1] = `${last.content[last.content.length - 1]}${text}`;
+        return;
+      }
+
+      if (last.content === undefined) {
+        last.content = [];
+      }
+
+      last.content.push(text);
+    }
+  }, options || defaultOptions);
+
+  parser.write(html);
+  parser.end();
+
+  return results;
+}
+
+function parserWrapper(...args) {
+  let option;
+
+  function parser(html) {
+    const opt = {...defaultOptions, ...option};
+    return postHTMLParser(html, opt);
+  }
+
+  if (
+    args.length === 1 &&
+    Boolean(args[0]) &&
+    args[0].constructor.name === 'Object'
+  ) {
+    option = args[0];
+    return parser;
+  }
+
+  option = args[1];
+  return parser(args[0]);
+}
+
+module.exports = parserWrapper;
+module.exports.defaultOptions = defaultOptions;
+module.exports.defaultDirectives = defaultDirectives;
diff --git a/packages/utils/posthtml-parser/package.json b/packages/utils/posthtml-parser/package.json
new file mode 100644
index 00000000000..b80ba4f2f09
--- /dev/null
+++ b/packages/utils/posthtml-parser/package.json
@@ -0,0 +1,45 @@
+{
+  "name": "@parcel/posthtml-parser",
+  "version": "0.6.0",
+  "description": "Parse HTML/XML to PostHTMLTree",
+  "keywords": [
+    "html",
+    "xml",
+    "parser",
+    "posthtml",
+    "posthtmltree"
+  ],
+  "main": "index.js",
+  "types": "index.d.ts",
+  "engines": {
+    "node": ">=10.0.0"
+  },
+  "repository": "posthtml/posthtml-parser",
+  "author": "Ivan Voischev <voischev.ivan@ya.ru>",
+  "contributors": [
+    {
+      "name": "Ivan Voischev",
+      "email": "voischev.ivan@ya.ru"
+    },
+    {
+      "name": "Ivan Demidov",
+      "email": "scrum@list.ru"
+    }
+  ],
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/posthtml/posthtml-parser/issues"
+  },
+  "homepage": "https://github.com/posthtml/posthtml-parser#readme",
+  "dependencies": {
+    "htmlparser2": "^5.0.1"
+  },
+  "funding": {
+    "type": "patreon",
+    "url": "https://opencollective.com/posthtml"
+  },
+  "collective": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/posthtml"
+  }
+}
diff --git a/yarn.lock b/yarn.lock
index 97468acae70..58d3ef9d62f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -5265,6 +5265,15 @@ dom-serializer@0:
     domelementtype "^2.0.1"
     entities "^2.0.0"
 
+dom-serializer@^1.0.1:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/dom-serializer/-/dom-serializer-1.1.0.tgz#5f7c828f1bfc44887dc2a315ab5c45691d544b58"
+  integrity sha512-ox7bvGXt2n+uLWtCRLybYx60IrOlWL/aCebWJk1T0d4m3y2tzf4U3ij9wBMUb6YJZpz06HCCYuyCDveE2xXmzQ==
+  dependencies:
+    domelementtype "^2.0.1"
+    domhandler "^3.0.0"
+    entities "^2.0.0"
+
 domain-browser@^1.1.1:
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/domain-browser/-/domain-browser-1.2.0.tgz#3d31f50191a6749dd1375a7f522e823d42e54eda"
@@ -5299,6 +5308,13 @@ domhandler@^2.3.0:
   dependencies:
     domelementtype "1"
 
+domhandler@^3.0.0, domhandler@^3.3.0:
+  version "3.3.0"
+  resolved "https://registry.yarnpkg.com/domhandler/-/domhandler-3.3.0.tgz#6db7ea46e4617eb15cf875df68b2b8524ce0037a"
+  integrity sha512-J1C5rIANUbuYK+FuFL98650rihynUOEzRLxW+90bKZRWB6A1X1Tf82GxR1qAWLyfNPRvjqfip3Q5tdYlmAa9lA==
+  dependencies:
+    domelementtype "^2.0.1"
+
 domutils@^1.5.1, domutils@^1.7.0:
   version "1.7.0"
   resolved "https://registry.yarnpkg.com/domutils/-/domutils-1.7.0.tgz#56ea341e834e06e6748af7a1cb25da67ea9f8c2a"
@@ -5307,6 +5323,15 @@ domutils@^1.5.1, domutils@^1.7.0:
     dom-serializer "0"
     domelementtype "1"
 
+domutils@^2.4.2:
+  version "2.4.2"
+  resolved "https://registry.yarnpkg.com/domutils/-/domutils-2.4.2.tgz#7ee5be261944e1ad487d9aa0616720010123922b"
+  integrity sha512-NKbgaM8ZJOecTZsIzW5gSuplsX2IWW2mIK7xVr8hTQF2v1CJWTmLZ1HOCh5sH+IzVPAGE5IucooOkvwBRAdowA==
+  dependencies:
+    dom-serializer "^1.0.1"
+    domelementtype "^2.0.1"
+    domhandler "^3.3.0"
+
 dot-prop@^3.0.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/dot-prop/-/dot-prop-3.0.0.tgz#1b708af094a49c9a0e7dbcad790aba539dac1177"
@@ -7396,6 +7421,16 @@ htmlparser2@^3.9.2:
     inherits "^2.0.1"
     readable-stream "^3.1.1"
 
+htmlparser2@^5.0.1:
+  version "5.0.1"
+  resolved "https://registry.yarnpkg.com/htmlparser2/-/htmlparser2-5.0.1.tgz#7daa6fc3e35d6107ac95a4fc08781f091664f6e7"
+  integrity sha512-vKZZra6CSe9qsJzh0BjBGXo8dvzNsq/oGvsjfRdOrrryfeD9UOBEEQdeoqCRmKZchF5h2zOBMQ6YuQ0uRUmdbQ==
+  dependencies:
+    domelementtype "^2.0.1"
+    domhandler "^3.3.0"
+    domutils "^2.4.2"
+    entities "^2.0.0"
+
 htmlparser2@~3.9.2:
   version "3.9.2"
   resolved "https://registry.yarnpkg.com/htmlparser2/-/htmlparser2-3.9.2.tgz#1bdf87acca0f3f9e53fa4fcceb0f4b4cbb00b338"