Show warning during build if page is returning a large amount of data (

#37264)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [x] Related issues linked using fixes #33829
- [x] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

packages/next/export/index.ts

@@ -385,6 +385,7 @@ export default async function exportApp(
       nextScriptWorkers: nextConfig.experimental.nextScriptWorkers,
       optimizeFonts: nextConfig.optimizeFonts,
       reactRoot: nextConfig.experimental.reactRoot || false,
+      largePageDataBytes: nextConfig.experimental.largePageDataBytes,
     }
 
     const { serverRuntimeConfig, publicRuntimeConfig } = nextConfig

packages/next/pages/_document.tsx

@@ -946,20 +946,20 @@ export class NextScript extends Component<OriginProps> {
   }
 
   static getInlineScriptSource(context: Readonly<HtmlProps>): string {
-    const { __NEXT_DATA__ } = context
+    const { __NEXT_DATA__, largePageDataBytes } = context
     try {
       const data = JSON.stringify(__NEXT_DATA__)
+      const bytes = Buffer.from(data).byteLength
+      const prettyBytes = require('../lib/pretty-bytes').default
 
-      if (process.env.NODE_ENV === 'development') {
-        const bytes = Buffer.from(data).byteLength
-        const prettyBytes = require('../lib/pretty-bytes').default
-        if (bytes > 128 * 1000) {
-          console.warn(
-            `Warning: data for page "${__NEXT_DATA__.page}" is ${prettyBytes(
-              bytes
-            )}, this amount of data can reduce performance.\nSee more info here: https://nextjs.org/docs/messages/large-page-data`
-          )
-        }
+      if (largePageDataBytes && bytes > largePageDataBytes) {
+        console.warn(
+          `Warning: data for page "${__NEXT_DATA__.page}" is ${prettyBytes(
+            bytes
+          )} which exceeds the threshold of ${prettyBytes(
+            largePageDataBytes
+          )}, this amount of data can reduce performance.\nSee more info here: https://nextjs.org/docs/messages/large-page-data`
+        )
       }
 
       return htmlEscapeJsonString(data)

packages/next/server/base-server.ts

@@ -177,6 +177,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     renderServerComponentData?: boolean
     serverComponentProps?: any
     reactRoot: boolean
+    largePageDataBytes?: number
   }
   protected serverOptions: ServerOptions
   private incrementalCache: IncrementalCache
@@ -327,6 +328,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
         ? this.nextConfig.crossOrigin
         : undefined,
       reactRoot: this.nextConfig.experimental.reactRoot === true,
+      largePageDataBytes: this.nextConfig.experimental.largePageDataBytes,
     }
 
     // Only the `publicRuntimeConfig` key is exposed to the client side

packages/next/server/config-shared.ts

@@ -135,6 +135,7 @@ export interface ExperimentalConfig {
   swcTraceProfiling?: boolean
   forceSwcTransforms?: boolean
   swcPlugins?: Array<[string, Record<string, unknown>]>
+  largePageDataBytes?: number
 }
 
 /**
@@ -516,6 +517,7 @@ export const defaultConfig: NextConfig = {
       remotePatterns: [],
     },
     forceSwcTransforms: false,
+    largePageDataBytes: 128 * 1000, // 128KB by default
   },
 }
 

packages/next/server/render.tsx

@@ -243,6 +243,7 @@ export type RenderOptsPartial = {
   crossOrigin?: string
   images: ImageConfigComplete
   reactRoot: boolean
+  largePageDataBytes?: number
 }
 
 export type RenderOpts = LoadComponentsReturnType & RenderOptsPartial
@@ -1562,6 +1563,7 @@ export async function renderToHTML(
     optimizeFonts: renderOpts.optimizeFonts,
     nextScriptWorkers: renderOpts.nextScriptWorkers,
     runtime: globalRuntime,
+    largePageDataBytes: renderOpts.largePageDataBytes,
   }
 
   const document = (

packages/next/shared/lib/html-context.ts

@@ -39,6 +39,7 @@ export type HtmlProps = {
   nextScriptWorkers?: boolean
   runtime?: 'edge' | 'nodejs'
   hasConcurrentFeatures?: boolean
+  largePageDataBytes?: number
 }
 
 export const HtmlContext = createContext<HtmlProps>(null as any)

test/e2e/prerender.test.ts

@@ -942,15 +942,15 @@ describe('Prerender', () => {
       })
     })
 
-    if ((global as any).isNextDev) {
-      it('should show warning when large amount of page data is returned', async () => {
-        await renderViaHTTP(next.url, '/large-page-data')
-        await check(
-          () => next.cliOutput,
-          /Warning: data for page "\/large-page-data" is 128 kB, this amount of data can reduce performance/
-        )
-      })
+    it('should show warning when large amount of page data is returned', async () => {
+      await renderViaHTTP(next.url, '/large-page-data')
+      await check(
+        () => next.cliOutput,
+        /Warning: data for page "\/large-page-data" is 256 kB which exceeds the threshold of 128 kB, this amount of data can reduce performance/
+      )
+    })
 
+    if ((global as any).isNextDev) {
       it('should not show warning from url prop being returned', async () => {
         const urlPropPage = 'pages/url-prop.js'
         await next.patchFile(

test/e2e/prerender/pages/large-page-data.js

@@ -4,7 +4,7 @@ import Link from 'next/link'
 export async function getStaticProps({ params }) {
   return {
     props: {
-      lotsOfData: new Array(128 * 1000).fill('a').join(''),
+      lotsOfData: new Array(256 * 1000).fill('a').join(''),
     },
     revalidate: false,
   }