vercel · timneutkens · Aug 22, 2023 · Jul 31, 2023 · Jul 31, 2023 · Jul 31, 2023
diff --git a/packages/next/src/client/components/app-router-announcer.tsx b/packages/next/src/client/components/app-router-announcer.tsx
@@ -57,7 +57,10 @@ export function AppRouterAnnouncer({ tree }: { tree: FlightRouterState }) {
 
     // Only announce the title change, but not for the first load because screen
     // readers do that automatically.
-    if (previousTitle.current !== undefined) {
+    if (
+      previousTitle.current !== undefined &&
+      previousTitle.current !== currentTitle
+    ) {
       setRouteAnnouncement(currentTitle)
     }
     previousTitle.current = currentTitle

diff --git a/packages/next/src/server/config-schema.ts b/packages/next/src/server/config-schema.ts
@@ -748,6 +748,7 @@ const configSchema = {
     },
     reactStrictMode: {
       type: 'boolean',
+      nullable: true,
     },
     redirects: {
       isFunction: true,

diff --git a/packages/next/src/server/config-shared.ts b/packages/next/src/server/config-shared.ts
@@ -682,7 +682,7 @@ export const defaultConfig: NextConfig = {
   serverRuntimeConfig: {},
   publicRuntimeConfig: {},
   reactProductionProfiling: false,
-  reactStrictMode: false,
+  reactStrictMode: null,
   httpAgentOptions: {
     keepAlive: true,
   },

diff --git a/test/development/app-dir/strict-mode-enabled-by-default/app/layout.js b/test/development/app-dir/strict-mode-enabled-by-default/app/layout.js
@@ -0,0 +1,7 @@
+export default function Root({ children }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}
diff --git a/test/development/app-dir/strict-mode-enabled-by-default/app/page.js b/test/development/app-dir/strict-mode-enabled-by-default/app/page.js
@@ -0,0 +1,9 @@
+'use client'
+import { useEffect } from 'react'
+
+let i = 1
+export default function Page() {
+  useEffect(() => {
+    console.log(`logged ${i++} times`)
+  }, [])
+}
diff --git a/...development/app-dir/strict-mode-enabled-by-default/strict-mode-enabled-by-default.test.ts b/...development/app-dir/strict-mode-enabled-by-default/strict-mode-enabled-by-default.test.ts
@@ -0,0 +1,23 @@
+import { createNextDescribe } from 'e2e-utils'
+import { BrowserInterface } from 'test/lib/browsers/base'
+
+createNextDescribe(
+  'Strict Mode enabled by default',
+  {
+    files: __dirname,
+  },
+  ({ next }) => {
+    // Recommended for tests that need a full browser
+    it('should work using browser', async () => {
+      const browser: BrowserInterface = await next.browser('/')
+      const logs = await browser.log()
+      const userLogs = logs.filter(
+        (log) => log.source === 'log' && log.message.match(/logged \d times/)
+      )
+      expect(userLogs.length).toBe(2)
+      userLogs.forEach((log, i) => {
+        expect(log.message).toBe(`logged ${i + 1} times`)
+      })
+    })
+  }
+)