Make sure polyfills are added for browsers without module support

packages/next/build/webpack/plugins/subresource-integrity-plugin.ts

@@ -17,17 +17,10 @@ export class SubresourceIntegrityPlugin {
           stage: webpack.Compilation.PROCESS_ASSETS_STAGE_ADDITIONS,
         },
         (assets) => {
-          // Collect all the entrypoint files.
+          // Collect all the assets.
           let files = new Set<string>()
-          for (const entrypoint of compilation.entrypoints.values()) {
-            const iterator = entrypoint?.getFiles()
-            if (!iterator) {
-              continue
-            }
-
-            for (const file of iterator) {
-              files.add(file)
-            }
+          for (const asset of compilation.getAssets()) {
+            files.add(asset.name)
           }
 
           // For each file, deduped, calculate the file hash.

packages/next/server/app-render.tsx

@@ -1287,6 +1287,16 @@ export async function renderToHTMLOrFlight(
         return flushed
       }
 
+      const polyfills = buildManifest.polyfillFiles
+        .filter(
+          (polyfill) =>
+            polyfill.endsWith('.js') && !polyfill.endsWith('.module.js')
+        )
+        .map((polyfill) => ({
+          src: `${renderOpts.assetPrefix || ''}/_next/${polyfill}`,
+          integrity: subresourceIntegrityManifest?.[polyfill],
+        }))
+
       try {
         const renderStream = await renderToInitialStream({
           ReactDOMServer,
@@ -1295,14 +1305,16 @@ export async function renderToHTMLOrFlight(
             onError: htmlRendererErrorHandler,
             nonce,
             // Include hydration scripts in the HTML
-            bootstrapScripts: subresourceIntegrityManifest
-              ? buildManifest.rootMainFiles.map((src) => ({
-                  src: `${renderOpts.assetPrefix || ''}/_next/` + src,
-                  integrity: subresourceIntegrityManifest[src],
-                }))
-              : buildManifest.rootMainFiles.map(
-                  (src) => `${renderOpts.assetPrefix || ''}/_next/` + src
-                ),
+            bootstrapScripts: [
+              ...(subresourceIntegrityManifest
+                ? buildManifest.rootMainFiles.map((src) => ({
+                    src: `${renderOpts.assetPrefix || ''}/_next/` + src,
+                    integrity: subresourceIntegrityManifest[src],
+                  }))
+                : buildManifest.rootMainFiles.map(
+                    (src) => `${renderOpts.assetPrefix || ''}/_next/` + src
+                  )),
+            ],
           },
         })
 
@@ -1311,6 +1323,7 @@ export async function renderToHTMLOrFlight(
           generateStaticHTML: generateStaticHTML,
           flushEffectHandler,
           flushEffectsToHead: true,
+          polyfills,
         })
       } catch (err: any) {
         // TODO-APP: show error overlay in development. `element` should probably be wrapped in AppRouter for this case.
@@ -1341,6 +1354,7 @@ export async function renderToHTMLOrFlight(
           generateStaticHTML: generateStaticHTML,
           flushEffectHandler,
           flushEffectsToHead: true,
+          polyfills,
         })
       }
     }

packages/next/server/node-web-streams-helper.ts

@@ -265,12 +265,14 @@ export async function continueFromInitialStream(
     generateStaticHTML,
     flushEffectHandler,
     flushEffectsToHead,
+    polyfills,
   }: {
     suffix?: string
     dataStream?: ReadableStream<Uint8Array>
     generateStaticHTML: boolean
     flushEffectHandler?: () => Promise<string>
     flushEffectsToHead: boolean
+    polyfills?: { src: string; integrity: string | undefined }[]
   }
 ): Promise<ReadableStream<Uint8Array>> {
   const closeTag = '</body></html>'
@@ -289,13 +291,26 @@ export async function continueFromInitialStream(
     dataStream ? createInlineDataStream(dataStream) : null,
     suffixUnclosed != null ? createSuffixStream(closeTag) : null,
     createHeadInjectionTransformStream(async () => {
+      // Inject polyfills for browsers that don't support modules. It has to be
+      // blocking here and can't be `defer` because other scripts have `async`.
+      const polyfillScripts = polyfills
+        ? polyfills
+            .map(
+              ({ src, integrity }) =>
+                `<script src="${src}" nomodule=""${
+                  integrity ? ` integrity="${integrity}"` : ''
+                }></script>`
+            )
+            .join('')
+        : ''
+
       // TODO-APP: Inject flush effects to end of head in app layout rendering, to avoid
       // hydration errors. Remove this once it's ready to be handled by react itself.
       const flushEffectsContent =
         flushEffectHandler && flushEffectsToHead
           ? await flushEffectHandler()
           : ''
-      return flushEffectsContent
+      return polyfillScripts + flushEffectsContent
     }),
   ].filter(nonNullable)
 

test/e2e/app-dir/index.test.ts

@@ -99,6 +99,13 @@ describe('app dir', () => {
       expect(html).toContain('hello from dynamic on client')
     })
 
+    it('should serve polyfills for browsers that do not support modules', async () => {
+      const html = await renderViaHTTP(next.url, '/dashboard/index')
+      expect(html).toMatch(
+        /<script src="\/_next\/static\/chunks\/polyfills(-\w+)?\.js" nomodule="">/
+      )
+    })
+
     // TODO-APP: handle css modules fouc in dev
     it.skip('should handle css imports in next/dynamic correctly', async () => {
       const browser = await webdriver(next.url, '/dashboard/index')