fix(nuxt)!: remove `__NUXT__` after hydration (#27745)

docs/1.getting-started/12.upgrade.md

@@ -371,6 +371,25 @@ However, if you are a module author using the `builder:watch` hook and wishing t
   })
 ```
 
+#### Removal of `window.__NUXT__` object
+
+##### What Changed
+
+We are removing the global `window.__NUXT__` object after the app finishes hydration.
+
+##### Reasons for Change
+
+This opens the way to multi-app patterns ([#21635](https://github.com/nuxt/nuxt/issues/21635)) and enables us to focus on a single way to access Nuxt app data - `useNuxtApp()`.
+
+##### Migration Steps
+
+The data is still available, but can be accessed with `useNuxtApp().payload`:
+
+```diff
+- console.log(window.__NUXT__)
++ console.log(useNuxtApp().payload)
+```
+
 #### Directory index scanning
 
 🚦 **Impact Level**: Medium

packages/nuxt/src/app/plugins/revive-payload.client.ts

@@ -49,7 +49,6 @@ export default defineNuxtPlugin({
       definePayloadReviver(reviver, revivers[reviver as keyof typeof revivers])
     }
     Object.assign(nuxtApp.payload, await nuxtApp.runWithContext(getNuxtClientPayload))
-    // For backwards compatibility - TODO: remove later
-    window.__NUXT__ = nuxtApp.payload
+    delete window.__NUXT__
   },
 })

packages/nuxt/src/core/templates.ts

@@ -267,7 +267,7 @@ declare module 'nitropack' {
 export const clientConfigTemplate: NuxtTemplate = {
   filename: 'nitro.client.mjs',
   getContents: () => `
-export const useRuntimeConfig = () => window?.__NUXT__?.config || {}
+export const useRuntimeConfig = () => window?.__NUXT__?.config || window?.useNuxtApp?.().payload?.config || {}
 `,
 }
 

test/bundle.test.ts

@@ -19,7 +19,7 @@ describe.skipIf(process.env.SKIP_BUNDLE_SIZE === 'true' || process.env.ECOSYSTEM
   for (const outputDir of ['.output', '.output-inline']) {
     it('default client bundle size', async () => {
       const clientStats = await analyzeSizes('**/*.js', join(rootDir, outputDir, 'public'))
-      expect.soft(roundToKilobytes(clientStats.totalBytes)).toMatchInlineSnapshot(`"106k"`)
+      expect.soft(roundToKilobytes(clientStats.totalBytes)).toMatchInlineSnapshot(`"107k"`)
       expect(clientStats.files.map(f => f.replace(/\..*\.js/, '.js'))).toMatchInlineSnapshot(`
         [
           "_nuxt/entry.js",

test/fixtures/basic/components/BreakInAsyncSetup.vue

@@ -3,7 +3,7 @@ async function getData () { }
 await getData()
 
 // break server-side
-const data = window.__NUXT__
+const data = window.useNuxtApp().payload
 </script>
 
 <template>

test/fixtures/basic/components/BreakInSetup.vue

@@ -1,6 +1,6 @@
 <script setup>
 // break server-side
-const data = window.__NUXT__
+const data = window.useNuxtApp().payload
 </script>
 
 <template>