Polyfill window.fetch by Default

packages/next/build/polyfills/fetch.js

@@ -0,0 +1 @@
+export default window.fetch

packages/next/build/webpack-config.ts

@@ -17,6 +17,7 @@ import { fileExists } from '../lib/file-exists'
 import { resolveRequest } from '../lib/resolve-request'
 import {
   CLIENT_STATIC_FILES_RUNTIME_MAIN,
+  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS,
   CLIENT_STATIC_FILES_RUNTIME_WEBPACK,
   REACT_LOADABLE_MANIFEST,
   SERVER_DIRECTORY,
@@ -54,6 +55,20 @@ const escapePathVariables = (value: any) => {
     : value
 }
 
+function getOptimizedAliases(isServer: boolean): { [pkg: string]: string } {
+  if (isServer) {
+    return {}
+  }
+
+  const stubWindowFetch = path.join(__dirname, 'polyfills', 'fetch.js')
+  return {
+    __internal_fetch: require.resolve('whatwg-fetch'),
+    unfetch$: stubWindowFetch,
+    'isomorphic-unfetch$': stubWindowFetch,
+    'whatwg-fetch$': stubWindowFetch,
+  }
+}
+
 export default async function getBaseWebpackConfig(
   dir: string,
   {
@@ -148,6 +163,10 @@ export default async function getBaseWebpackConfig(
               dev ? `next-dev.js` : 'next.js'
             )
           ),
+        [CLIENT_STATIC_FILES_RUNTIME_POLYFILLS]: path.join(
+          NEXT_PROJECT_ROOT_DIST_CLIENT,
+          'polyfills.js'
+        ),
       }
     : undefined
 
@@ -196,6 +215,7 @@ export default async function getBaseWebpackConfig(
       next: NEXT_PROJECT_ROOT,
       [PAGES_DIR_ALIAS]: pagesDir,
       [DOT_NEXT_ALIAS]: distDir,
+      ...getOptimizedAliases(isServer),
     },
     mainFields: isServer ? ['main', 'module'] : ['browser', 'module', 'main'],
     plugins: [PnpWebpackPlugin],
@@ -531,7 +551,8 @@ export default async function getBaseWebpackConfig(
         if (
           !dev &&
           (chunk.name === CLIENT_STATIC_FILES_RUNTIME_MAIN ||
-            chunk.name === CLIENT_STATIC_FILES_RUNTIME_WEBPACK)
+            chunk.name === CLIENT_STATIC_FILES_RUNTIME_WEBPACK ||
+            chunk.name === CLIENT_STATIC_FILES_RUNTIME_POLYFILLS)
         ) {
           return chunk.name.replace(/\.js$/, '-[contenthash].js')
         }

packages/next/build/webpack/plugins/build-manifest-plugin.ts

@@ -1,13 +1,15 @@
 import devalue from 'devalue'
+import { Compiler } from 'webpack'
+import { RawSource } from 'webpack-sources'
+
 import {
   BUILD_MANIFEST,
   CLIENT_STATIC_FILES_PATH,
   CLIENT_STATIC_FILES_RUNTIME_MAIN,
+  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS,
   IS_BUNDLED_PAGE_REGEX,
   ROUTE_NAME_REGEX,
 } from '../../../next-server/lib/constants'
-import { Compiler } from 'webpack'
-import { RawSource } from 'webpack-sources'
 
 interface AssetMap {
   devFiles: string[]
@@ -27,7 +29,7 @@ const generateClientManifest = (
   const appDependencies = new Set(assetMap.pages['/_app'])
 
   Object.entries(assetMap.pages).forEach(([page, dependencies]) => {
-    if (page === '/_app') return
+    if (page === '/_app' || page === '/_polyfills') return
     // Filter out dependencies in the _app entry, because those will have already
     // been loaded by the client prior to a navigation event
     const filteredDeps = dependencies.filter(
@@ -74,6 +76,11 @@ export default class BuildManifestPlugin {
             ? mainJsChunk.files.filter((file: string) => /\.js$/.test(file))
             : []
 
+        const polyfillChunk = chunks.find(
+          c => c.name === CLIENT_STATIC_FILES_RUNTIME_POLYFILLS
+        )
+        const polyfillFiles: string[] = polyfillChunk ? polyfillChunk.files : []
+
         for (const filePath of Object.keys(compilation.assets)) {
           const path = filePath.replace(/\\/g, '/')
           if (/^static\/development\/dll\//.test(path)) {
@@ -125,6 +132,9 @@ export default class BuildManifestPlugin {
           assetMap.pages['/'] = assetMap.pages['/index']
         }
 
+        // Create a separate entry  for polyfills
+        assetMap.pages['/_polyfills'] = polyfillFiles
+
         // Add the runtime build manifest file (generated later in this file)
         // as a dependency for the app. If the flag is false, the file won't be
         // downloaded by the client.

packages/next/client/polyfills.js

@@ -0,0 +1 @@
+import '__internal_fetch'

packages/next/next-server/lib/constants.ts

@@ -21,6 +21,8 @@ export const CLIENT_STATIC_FILES_RUNTIME_MAIN = `${CLIENT_STATIC_FILES_RUNTIME_P
 export const CLIENT_STATIC_FILES_RUNTIME_AMP = `${CLIENT_STATIC_FILES_RUNTIME_PATH}/amp.js`
 // static/runtime/webpack.js
 export const CLIENT_STATIC_FILES_RUNTIME_WEBPACK = `${CLIENT_STATIC_FILES_RUNTIME_PATH}/webpack.js`
+// static/runtime/polyfills.js
+export const CLIENT_STATIC_FILES_RUNTIME_POLYFILLS = `${CLIENT_STATIC_FILES_RUNTIME_PATH}/polyfills.js`
 // matches static/<buildid>/pages/<page>.js
 export const IS_BUNDLED_PAGE_REGEX = /^static[/\\][^/\\]+[/\\]pages.*\.js$/
 // matches static/<buildid>/pages/:page*.js

packages/next/next-server/lib/utils.ts

@@ -150,6 +150,7 @@ export type DocumentProps = DocumentInitialProps & {
   hasCssMode: boolean
   devFiles: string[]
   files: string[]
+  polyfillFiles: string[]
   dynamicImports: ManifestItem[]
   assetPrefix?: string
   canonicalBase: string

packages/next/next-server/server/render.tsx

@@ -188,6 +188,7 @@ function renderDocument(
     staticMarkup,
     devFiles,
     files,
+    polyfillFiles,
     dynamicImports,
     htmlProps,
     bodyTags,
@@ -207,6 +208,7 @@ function renderDocument(
     dynamicImports: ManifestItem[]
     files: string[]
     devFiles: string[]
+    polyfillFiles: string[]
     htmlProps: any
     bodyTags: any
     headTags: any
@@ -242,6 +244,7 @@ function renderDocument(
           staticMarkup,
           devFiles,
           files,
+          polyfillFiles,
           dynamicImports,
           assetPrefix,
           htmlProps,
@@ -488,6 +491,7 @@ export async function renderToHTML(
       ...getPageFiles(buildManifest, '/_app'),
     ]),
   ]
+  const polyfillFiles = getPageFiles(buildManifest, '/_polyfills')
 
   const renderElementToString = staticMarkup
     ? renderToStaticMarkup
@@ -642,6 +646,7 @@ export async function renderToHTML(
     dynamicImports,
     files,
     devFiles,
+    polyfillFiles,
   })
 
   if (inAmpMode && html) {

packages/next/package.json

@@ -127,7 +127,8 @@
     "webpack": "4.39.0",
     "webpack-dev-middleware": "3.7.0",
     "webpack-hot-middleware": "2.25.0",
-    "webpack-sources": "1.4.3"
+    "webpack-sources": "1.4.3",
+    "whatwg-fetch": "3.0.0"
   },
   "peerDependencies": {
     "react": "^16.6.0",

packages/next/pages/_document.tsx

@@ -596,6 +596,25 @@ export class NextScript extends Component<OriginProps> {
     })
   }
 
+  getPolyfillScripts() {
+    // polyfills.js has to be rendered as nomodule without async
+    // It also has to be the first script to load
+    const { assetPrefix, polyfillFiles } = this.context._documentProps
+    const { _devOnlyInvalidateCacheQueryString } = this.context
+
+    return polyfillFiles
+      .filter(polyfill => !/\.module\.js$/.test(polyfill))
+      .map(polyfill => (
+        <script
+          key={polyfill}
+          nonce={this.props.nonce}
+          crossOrigin={this.props.crossOrigin || process.crossOrigin}
+          noModule={true}
+          src={`${assetPrefix}/_next/${polyfill}${_devOnlyInvalidateCacheQueryString}`}
+        />
+      ))
+  }
+
   static getInlineScriptSource(documentProps: DocumentProps) {
     const { __NEXT_DATA__ } = documentProps
     try {
@@ -784,6 +803,7 @@ export class NextScript extends Component<OriginProps> {
             }}
           />
         ) : null}
+        {this.getPolyfillScripts()}
         {page !== '/_error' && pageScript}
         {appScript}
         {staticMarkup ? null : this.getDynamicChunks()}

test/integration/build-stats-output/test/index.test.js

@@ -9,6 +9,6 @@ const appDir = join(__dirname, '../react-site')
 describe('Build Stats Output', () => {
   it('Shows correct package count in output', async () => {
     const { stdout } = await nextBuild(appDir, undefined, { stdout: true })
-    expect(stdout).toMatch(/\/something .*?4/)
+    expect(stdout).toMatch(/\/something .*?2/)
   })
 })

test/integration/defer-scripts/test/index.test.js

@@ -38,9 +38,10 @@ describe('Defer Scripts', () => {
     let missing = false
 
     for (const script of $('script').toArray()) {
-      const { defer, type } = script.attribs
+      const { defer, type, src } = script.attribs
       // application/json doesn't need defer
-      if (type === 'application/json') {
+      // polyfills cannot be deferred or async'd
+      if (type === 'application/json' || src.includes('polyfills')) {
         continue
       }
 

yarn.lock

@@ -15264,7 +15264,7 @@ [email protected]:
   resolved "https://registry.yarnpkg.com/whatwg-fetch/-/whatwg-fetch-2.0.4.tgz#dde6a5df315f9d39991aa17621853d720b85566f"
   integrity sha512-dcQ1GWpOD/eEQ97k66aiEVpNnapVj90/+R+SXTPYGHpYBBypfKJEQjLrvMZ7YXbKm21gXd4NcuxUTjiv1YtLng==
 
-whatwg-fetch@>=0.10.0:
+whatwg-fetch@3.0.0, whatwg-fetch@>=0.10.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/whatwg-fetch/-/whatwg-fetch-3.0.0.tgz#fc804e458cc460009b1a2b966bc8817d2578aefb"
   integrity sha512-9GSJUgz1D4MfyKU7KRqwOjXCXTqWdFNvEr7eUBYchQiVc744mqK/MzXPNR2WsPkmkOa4ywfg8C2n8h+13Bey1Q==