module: unflag import assertions

doc/api/errors.md

@@ -1108,6 +1108,14 @@ The JS execution context is not associated with a Node.js environment.
 This may occur when Node.js is used as an embedded library and some hooks
 for the JS engine are not set up properly.
 
+<a id="ERR_FAILED_IMPORT_ASSERTION"></a>
+### `ERR_FAILED_IMPORT_ASSERTION`
+<!-- YAML
+added: REPLACEME
+-->
+
+An import assertion has failed, preventing the specified module to be imported.
+
 <a id="ERR_FALSY_VALUE_REJECTION"></a>
 ### `ERR_FALSY_VALUE_REJECTION`
 
@@ -1659,6 +1667,14 @@ for more information.
 
 An invalid HTTP token was supplied.
 
+<a id="ERR_INVALID_IMPORT_ASSERTION"></a>
+### `ERR_INVALID_IMPORT_ASSERTION`
+<!-- YAML
+added: REPLACEME
+-->
+
+An import assertion is not supported by this version of Node.js.
+
 <a id="ERR_INVALID_IP_ADDRESS"></a>
 ### `ERR_INVALID_IP_ADDRESS`
 

doc/api/esm.md

@@ -5,6 +5,9 @@
 <!-- YAML
 added: v8.5.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Add support for import assertions.
   - version:
     - REPLACEME
     pr-url: https://github.com/nodejs/node/pull/37468
@@ -228,6 +231,25 @@ absolute URL strings.
 import fs from 'node:fs/promises';
 ```
 
+## Import assertions
+<!-- YAML
+added: REPLACEME
+-->
+
+The [Import Assertions proposal][] adds an inline syntax for module import
+statements to pass on more information alongside the module specifier.
+
+```js
+import json from './foo.json' assert { type: "json" };
+await import('foo.json', { assert: { type: "json" } });
+```
+
+Node.js supports the following `type` values:
+
+| `type`   | Resolves to      |
+| -------- | ---------------- |
+| `"json"` | [JSON modules][] |
+
 ## Builtin modules
 
 [Core modules][] provide named exports of their public API. A
@@ -516,9 +538,8 @@ same path.
 
 Assuming an `index.mjs` with
 
-<!-- eslint-skip -->
 ```js
-import packageConfig from './package.json';
+import packageConfig from './package.json' assert { type: 'json' };
 ```
 
 The `--experimental-json-modules` flag is needed for the module
@@ -1367,6 +1388,8 @@ success!
 [Dynamic `import()`]: https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#Dynamic_Imports
 [ECMAScript Top-Level `await` proposal]: https://github.com/tc39/proposal-top-level-await/
 [ES Module Integration Proposal for Web Assembly]: https://github.com/webassembly/esm-integration
+[Import Assertions proposal]: https://github.com/tc39/proposal-import-assertions
+[JSON modules]: #json-modules
 [Node.js Module Resolution Algorithm]: #resolver-algorithm-specification
 [Terminology]: #terminology
 [URL]: https://url.spec.whatwg.org/

doc/api/vm.md

@@ -54,6 +54,10 @@ executed in specific contexts.
 <!-- YAML
 added: v0.3.1
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Added suppoort of import assertions to the
+                 `importModuleDynamically` parameter.
   - version: v10.6.0
     pr-url: https://github.com/nodejs/node/pull/20300
     description: The `produceCachedData` is deprecated in favour of
@@ -91,6 +95,8 @@ changes:
     using it in a production environment.
     * `specifier` {string} specifier passed to `import()`
     * `script` {vm.Script}
+    * `import_assertions` {Object} The `"assert"` value passed to the
+      `optionExpression` optional parameter.
     * Returns: {Module Namespace Object|vm.Module} Returning a `vm.Module` is
       recommended in order to take advantage of error tracking, and to avoid
       issues with namespaces that contain `then` function exports.
@@ -642,6 +648,13 @@ The `vm.SourceTextModule` class provides the [Source Text Module Record][] as
 defined in the ECMAScript specification.
 
 ### `new vm.SourceTextModule(code[, options])`
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Added suppoort of import assertions to the
+                 `importModuleDynamically` parameter.
+-->
 
 * `code` {string} JavaScript Module code to parse
 * `options`
@@ -667,6 +680,8 @@ defined in the ECMAScript specification.
     `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`][].
     * `specifier` {string} specifier passed to `import()`
     * `module` {vm.Module}
+    * `import_assertions` {Object} The `"assert"` value passed to the
+      `optionExpression` optional parameter.
     * Returns: {Module Namespace Object|vm.Module} Returning a `vm.Module` is
       recommended in order to take advantage of error tracking, and to avoid
       issues with namespaces that contain `then` function exports.
@@ -852,6 +867,10 @@ const vm = require('vm');
 <!-- YAML
 added: v10.10.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Added suppoort of import assertions to the
+                 `importModuleDynamically` parameter.
   - version: v15.9.0
     pr-url: https://github.com/nodejs/node/pull/35431
     description: Added `importModuleDynamically` option again.
@@ -893,6 +912,8 @@ changes:
     considered stable.
     * `specifier` {string} specifier passed to `import()`
     * `function` {Function}
+    * `import_assertions` {Object} The `"assert"` value passed to the
+      `optionExpression` optional parameter.
     * Returns: {Module Namespace Object|vm.Module} Returning a `vm.Module` is
       recommended in order to take advantage of error tracking, and to avoid
       issues with namespaces that contain `then` function exports.
@@ -1068,6 +1089,10 @@ vm.measureMemory({ mode: 'detailed', execution: 'eager' })
 <!-- YAML
 added: v0.3.1
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Added suppoort of import assertions to the
+                 `importModuleDynamically` parameter.
   - version: v6.3.0
     pr-url: https://github.com/nodejs/node/pull/6635
     description: The `breakOnSigint` option is supported now.
@@ -1113,6 +1138,8 @@ changes:
     using it in a production environment.
     * `specifier` {string} specifier passed to `import()`
     * `script` {vm.Script}
+    * `import_assertions` {Object} The `"assert"` value passed to the
+      `optionExpression` optional parameter.
     * Returns: {Module Namespace Object|vm.Module} Returning a `vm.Module` is
       recommended in order to take advantage of error tracking, and to avoid
       issues with namespaces that contain `then` function exports.
@@ -1145,6 +1172,10 @@ console.log(contextObject);
 <!-- YAML
 added: v0.3.1
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Added suppoort of import assertions to the
+                 `importModuleDynamically` parameter.
   - version: v14.6.0
     pr-url: https://github.com/nodejs/node/pull/34023
     description: The `microtaskMode` option is supported now.
@@ -1211,6 +1242,8 @@ changes:
     using it in a production environment.
     * `specifier` {string} specifier passed to `import()`
     * `script` {vm.Script}
+    * `import_assertions` {Object} The `"assert"` value passed to the
+      `optionExpression` optional parameter.
     * Returns: {Module Namespace Object|vm.Module} Returning a `vm.Module` is
       recommended in order to take advantage of error tracking, and to avoid
       issues with namespaces that contain `then` function exports.
@@ -1247,6 +1280,10 @@ console.log(contextObject);
 <!-- YAML
 added: v0.3.1
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Added suppoort of import assertions to the
+                 `importModuleDynamically` parameter.
   - version: v6.3.0
     pr-url: https://github.com/nodejs/node/pull/6635
     description: The `breakOnSigint` option is supported now.
@@ -1290,6 +1327,8 @@ changes:
     using it in a production environment.
     * `specifier` {string} specifier passed to `import()`
     * `script` {vm.Script}
+    * `import_assertions` {Object} The `"assert"` value passed to the
+      `optionExpression` optional parameter.
     * Returns: {Module Namespace Object|vm.Module} Returning a `vm.Module` is
       recommended in order to take advantage of error tracking, and to avoid
       issues with namespaces that contain `then` function exports.

lib/internal/errors.js

@@ -953,6 +953,9 @@ E('ERR_ENCODING_NOT_SUPPORTED', 'The "%s" encoding is not supported',
   RangeError);
 E('ERR_EVAL_ESM_CANNOT_PRINT', '--print cannot be used with ESM input', Error);
 E('ERR_EVENT_RECURSION', 'The event "%s" is already being dispatched', Error);
+E('ERR_FAILED_IMPORT_ASSERTION', (request, key, expectedValue, actualValue) => {
+  return `Failed to load module "${request}", expected ${key} to be ${JSONStringify(expectedValue)}, got ${JSONStringify(actualValue)} instead`;
+}, TypeError);
 E('ERR_FALSY_VALUE_REJECTION', function(reason) {
   this.reason = reason;
   return 'Promise was rejected with falsy value';
@@ -1250,6 +1253,9 @@ E('ERR_INVALID_FILE_URL_HOST',
 E('ERR_INVALID_FILE_URL_PATH', 'File URL path %s', TypeError);
 E('ERR_INVALID_HANDLE_TYPE', 'This handle type cannot be sent', TypeError);
 E('ERR_INVALID_HTTP_TOKEN', '%s must be a valid HTTP token ["%s"]', TypeError);
+E('ERR_INVALID_IMPORT_ASSERTION',
+  (type, value) => `Invalid ${JSONStringify(type)} import assertion: ${JSONStringify(value)}`,
+  TypeError);
 E('ERR_INVALID_IP_ADDRESS', 'Invalid IP address: %s', TypeError);
 E('ERR_INVALID_MODULE_SPECIFIER', (request, reason, base = undefined) => {
   return `Invalid module "${request}" ${reason}${base ?

lib/internal/modules/cjs/loader.js

@@ -1021,9 +1021,10 @@ function wrapSafe(filename, content, cjsModuleInstance) {
       filename,
       lineOffset: 0,
       displayErrors: true,
-      importModuleDynamically: async (specifier) => {
+      importModuleDynamically: async (specifier, _, import_assertions) => {
         const loader = asyncESM.esmLoader;
-        return loader.import(specifier, normalizeReferrerURL(filename));
+        return loader.import(specifier, normalizeReferrerURL(filename),
+                             import_assertions);
       },
     });
   }
@@ -1036,9 +1037,10 @@ function wrapSafe(filename, content, cjsModuleInstance) {
       '__dirname',
     ], {
       filename,
-      importModuleDynamically(specifier) {
+      importModuleDynamically(specifier, _, import_assertions) {
         const loader = asyncESM.esmLoader;
-        return loader.import(specifier, normalizeReferrerURL(filename));
+        return loader.import(specifier, normalizeReferrerURL(filename),
+                             import_assertions);
       },
     });
   } catch (err) {

lib/internal/modules/esm/loader.js

@@ -6,11 +6,13 @@ require('internal/modules/cjs/loader');
 const {
   Array,
   ArrayIsArray,
+  ArrayPrototypeIncludes,
   ArrayPrototypeJoin,
   ArrayPrototypePush,
   FunctionPrototypeBind,
   FunctionPrototypeCall,
   ObjectCreate,
+  ObjectFreeze,
   ObjectSetPrototypeOf,
   PromiseAll,
   RegExpPrototypeExec,
@@ -20,8 +22,10 @@ const {
 } = primordials;
 
 const {
+  ERR_FAILED_IMPORT_ASSERTION,
   ERR_INVALID_ARG_TYPE,
   ERR_INVALID_ARG_VALUE,
+  ERR_INVALID_IMPORT_ASSERTION,
   ERR_INVALID_MODULE_SPECIFIER,
   ERR_INVALID_RETURN_PROPERTY_VALUE,
   ERR_INVALID_RETURN_VALUE,
@@ -44,6 +48,10 @@ const { translators } = require(
   'internal/modules/esm/translators');
 const { getOptionValue } = require('internal/options');
 
+const importAssertionTypeCache = new SafeWeakMap();
+const finalFormatCache = new SafeWeakMap();
+const supportedTypes = ObjectFreeze([undefined, 'json']);
+
 /**
  * An ESMLoader instance is used as the main entry point for loading ES modules.
  * Currently, this is a singleton -- there is only one used for loading
@@ -202,33 +210,66 @@ class ESMLoader {
       const { ModuleWrap, callbackMap } = internalBinding('module_wrap');
       const module = new ModuleWrap(url, undefined, source, 0, 0);
       callbackMap.set(module, {
-        importModuleDynamically: (specifier, { url }) => {
-          return this.import(specifier, url);
+        importModuleDynamically: (specifier, { url }, import_assertions) => {
+          return this.import(specifier, url, import_assertions);
         }
       });
 
       return module;
     };
     const job = new ModuleJob(this, url, evalInstance, false, false);
     this.moduleMap.set(url, job);
+    finalFormatCache.set(job, 'module');
     const { module } = await job.run();
 
     return {
       namespace: module.getNamespace(),
     };
   }
 
-  async getModuleJob(specifier, parentURL) {
+  async getModuleJob(specifier, parentURL, import_assertions) {
+    if (!ArrayPrototypeIncludes(supportedTypes, import_assertions.type)) {
+      throw new ERR_INVALID_IMPORT_ASSERTION('type', import_assertions.type);
+    }
+
     const { format, url } = await this.resolve(specifier, parentURL);
     let job = this.moduleMap.get(url);
     // CommonJS will set functions for lazy job evaluation.
     if (typeof job === 'function') this.moduleMap.set(url, job = job());
 
-    if (job !== undefined) return job;
+    if (job != null) {
+      const currentImportAssertionType = importAssertionTypeCache.get(job);
+      if (currentImportAssertionType === import_assertions.type) return job;
+
+      try {
+        // To avoid race conditions, wait for previous module to fulfill first.
+        await job.modulePromise;
+      } catch {
+        // If the other job failed with a different `type` assertion, we got
+        // another chance.
+        job = undefined;
+      }
+
+      if (job !== undefined) {
+        const finalFormat = finalFormatCache.get(job);
+        if (
+          import_assertions.type == null ||
+              (import_assertions.type === 'json' && finalFormat === 'json')
+        ) return job;
+        throw new ERR_FAILED_IMPORT_ASSERTION(
+          url, 'type', import_assertions.type, finalFormat);
+      }
+    }
 
     const moduleProvider = async (url, isMain) => {
       const { format: finalFormat, source } = await this.load(url, { format });
 
+      if (import_assertions.type === 'json' && finalFormat !== 'json') {
+        throw new ERR_FAILED_IMPORT_ASSERTION(
+          url, 'type', import_assertions.type, finalFormat);
+      }
+      finalFormatCache.set(job, finalFormat);
+
       const translator = translators.get(finalFormat);
 
       if (!translator) throw new ERR_UNKNOWN_MODULE_FORMAT(finalFormat);
@@ -249,6 +290,7 @@ class ESMLoader {
       inspectBrk
     );
 
+    importAssertionTypeCache.set(job, import_assertions.type);
     this.moduleMap.set(url, job);
 
     return job;
@@ -262,18 +304,19 @@ class ESMLoader {
    * loader module.
    *
    * @param {string | string[]} specifiers Path(s) to the module
-   * @param {string} [parentURL] Path of the parent importing the module
-   * @returns {object | object[]} A list of module export(s)
+   * @param {string} parentURL Path of the parent importing the module
+   * @param {Record<string, Record<string, string>>} import_assertions
+   * @returns {Promise<object | object[]>} A list of module export(s)
    */
-  async import(specifiers, parentURL) {
+  async import(specifiers, parentURL, import_assertions) {
     const wasArr = ArrayIsArray(specifiers);
     if (!wasArr) specifiers = [specifiers];
 
     const count = specifiers.length;
     const jobs = new Array(count);
 
     for (let i = 0; i < count; i++) {
-      jobs[i] = this.getModuleJob(specifiers[i], parentURL)
+      jobs[i] = this.getModuleJob(specifiers[i], parentURL, import_assertions)
         .then((job) => job.run())
         .then(({ module }) => module.getNamespace());
     }