feat: add option to output only legacy builds

README.md

@@ -133,6 +133,13 @@ export default {
 
   Defaults to `false`. Enabling this option will exclude `systemjs/dist/s.min.js` inside polyfills-legacy chunk.
 
+### `renderModernChunks`
+
+- **Type:** `boolean`
+- **Default:** `true`
+
+  Set to `false` to only output the legacy bundles that support all target browsers.
+
 ## Browsers that supports ESM but does not support widely-available features
 
 The legacy plugin offers a way to use widely-available features natively in the modern build, while falling back to the legacy build in browsers with native ESM but without those features supported (e.g. Legacy Edge). This feature works by injecting a runtime check and loading the legacy bundle with SystemJs runtime if needed. There are the following drawbacks:

src/index.ts

@@ -134,6 +134,12 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
   let targets: Options['targets']
 
   const genLegacy = options.renderLegacyChunks !== false
+  const genModern = options.renderModernChunks !== false
+  if (!genLegacy && !genModern) {
+    throw new Error(
+      '`renderLegacyChunks` and `renderModernChunks` cannot be both false',
+    )
+  }
 
   const debugFlags = (process.env.DEBUG ?? '').split(',')
   const isDebug
@@ -145,7 +151,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
   const modernPolyfills = new Set<string>()
   const legacyPolyfills = new Set<string>()
 
-  if (Array.isArray(options.modernPolyfills)) {
+  if (Array.isArray(options.modernPolyfills) && genModern) {
     options.modernPolyfills.forEach((i) => {
       modernPolyfills.add(
         i.includes('/') ? `core-js/${i}` : `core-js/modules/${i}.js`,
@@ -360,9 +366,15 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
       const { rollupOptions } = resolvedConfig.build
       const { output } = rollupOptions
       if (Array.isArray(output)) {
-        rollupOptions.output = [...output.map(createLegacyOutput), ...output]
+        rollupOptions.output = [
+          ...output.map(createLegacyOutput),
+          ...(genModern ? output : []),
+        ]
       } else {
-        rollupOptions.output = [createLegacyOutput(output), output ?? {}]
+        rollupOptions.output = [
+          createLegacyOutput(output),
+          ...(genModern ? [output || {}] : []),
+        ]
       }
     },
 
@@ -374,7 +386,8 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
       if (!isLegacyChunk(chunk, opts)) {
         if (
           options.modernPolyfills
-          && !Array.isArray(options.modernPolyfills)
+          && !Array.isArray(options.modernPolyfills) &&
+          genModern
         ) {
           // analyze and record modern polyfills
           await detectPolyfills(raw, 'supports es6-module', modernPolyfills)
@@ -497,50 +510,59 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
       if (resolvedConfig.build.ssr) return
       if (!chunk) return
       if (chunk.fileName.includes('-legacy')) {
-        // The legacy bundle is built first, and its index.html isn't actually
-        // emitted. Here we simply record its corresponding legacy chunk.
+        // The legacy bundle is built first, and its index.html isn't actually emitted if
+        // modern bundle will be generated. Here we simply record its corresponding legacy chunk.
         facadeToLegacyChunkMap.set(chunk.facadeModuleId, chunk.fileName)
-        return
+        if (genModern) {
+          return
+        }
+      }
+      if (!genModern) {
+        html = html.replace(/<script type="module".*?<\/script>/g, '')
       }
 
       const tags: HtmlTagDescriptor[] = []
       const htmlFilename = chunk.facadeModuleId?.replace(/\?.*$/, '')
 
       // 1. inject modern polyfills
-      const modernPolyfillFilename = facadeToModernPolyfillMap.get(
-        chunk.facadeModuleId,
-      )
-
-      if (modernPolyfillFilename) {
-        tags.push({
-          tag: 'script',
-          attrs: {
-            type: 'module',
-            crossorigin: true,
-            src: toAssetPathFromHtml(
-              modernPolyfillFilename,
-              chunk.facadeModuleId!,
-              resolvedConfig,
-            ),
-          },
-        })
-      } else if (modernPolyfills.size) {
-        throw new Error(
-          `No corresponding modern polyfill chunk found for ${htmlFilename}`,
+      if (genModern) {
+        const modernPolyfillFilename = facadeToModernPolyfillMap.get(
+          chunk.facadeModuleId,
         )
+
+        if (modernPolyfillFilename) {
+          tags.push({
+            tag: 'script',
+            attrs: {
+              type: 'module',
+              crossorigin: true,
+              src: toAssetPathFromHtml(
+                modernPolyfillFilename,
+                chunk.facadeModuleId!,
+                resolvedConfig,
+              ),
+            },
+          })
+        } else if (modernPolyfills.size) {
+          throw new Error(
+            `No corresponding modern polyfill chunk found for ${htmlFilename}`,
+          )
+        }
       }
 
       if (!genLegacy) {
         return { html, tags }
       }
 
       // 2. inject Safari 10 nomodule fix
-      tags.push({
-        tag: 'script',
-        attrs: { nomodule: true },
-        children: safari10NoModuleFix,
-        injectTo: 'body',
-      })
+      if (genModern) {
+        tags.push({
+          tag: 'script',
+          attrs: { nomodule: true },
+          children: safari10NoModuleFix,
+          injectTo: 'body',
+        })
+      }
 
       // 3. inject legacy polyfills
       const legacyPolyfillFilename = facadeToLegacyPolyfillMap.get(
@@ -550,7 +572,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
         tags.push({
           tag: 'script',
           attrs: {
-            nomodule: true,
+            nomodule: genModern,
             crossorigin: true,
             id: legacyPolyfillId,
             src: toAssetPathFromHtml(
@@ -576,7 +598,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
         tags.push({
           tag: 'script',
           attrs: {
-            nomodule: true,
+            nomodule: genModern,
             crossorigin: true,
             // we set the entry path on the element as an attribute so that the
             // script content will stay consistent - which allows using a constant
@@ -598,7 +620,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
       }
 
       // 5. inject dynamic import fallback entry
-      if (/* genLegacy && */legacyPolyfillFilename && legacyEntryFilename) {
+      if (legacyPolyfillFilename && legacyEntryFilename && genModern) {
         tags.push({
           tag: 'script',
           attrs: { type: 'module' },
@@ -624,7 +646,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
         return
       }
 
-      if (isLegacyBundle(bundle, opts)) {
+      if (isLegacyBundle(bundle, opts) && genModern) {
         // avoid emitting duplicate assets
         for (const name of Object.keys(bundle)) {
           if (bundle[name].type === 'asset' && !/.+\.map$/.test(name)) {

src/types.ts

@@ -24,4 +24,8 @@ export interface Options {
    * default: false
    */
   externalSystemJS?: boolean,
+  /**
+   * default: true
+   */
+  renderModernChunks?: boolean
 }