fix(vue-app): fix asyncData memory leak on client-side (#4966)

Co-authored-by: Sébastien Chopin <seb@chopin.io>

packages/vue-app/template/utils.js

@@ -1,7 +1,5 @@
 import Vue from 'vue'
 
-const noopData = () => ({})
-
 // window.{{globals.loadedCallback}} hook
 // Useful for jsdom testing or plugins (https://github.com/tmpvar/jsdom#dealing-with-asynchronous-script-loading)
 if (process.client) {
@@ -24,12 +22,17 @@ export function interopDefault(promise) {
 }
 
 export function applyAsyncData(Component, asyncData) {
-  const ComponentData = Component.options.data || noopData
-  // Prevent calling this method for each request on SSR context
-  if (!asyncData && Component.options.hasAsyncData) {
+  if (
+    // For SSR, we once all this function without second param to just apply asyncData
+    // Prevent doing this for each SSR request
+    !asyncData && Component.options.__hasNuxtData
+  ) {
     return
   }
-  Component.options.hasAsyncData = true
+
+  const ComponentData = Component.options._originDataFn || Component.options.data || function () { return {} }
+  Component.options._originDataFn = ComponentData
+
   Component.options.data = function () {
     const data = ComponentData.call(this)
     if (this.$ssrContext) {
@@ -37,6 +40,9 @@ export function applyAsyncData(Component, asyncData) {
     }
     return { ...data, ...asyncData }
   }
+
+  Component.options.__hasNuxtData = true
+
   if (Component._Ctor && Component._Ctor.options) {
     Component._Ctor.options.data = Component.options.data
   }

test/fixtures/spa/pages/async.vue

@@ -0,0 +1,20 @@
+<template>
+  <pre>
+    {{ debug }}
+  </pre>
+</template>
+
+<script>
+export default {
+  asyncData() {
+    return {
+      [Math.random()]: true
+    }
+  },
+  computed: {
+    debug() {
+      return JSON.stringify(this.$data, null, 2)
+    }
+  }
+}
+</script>

test/unit/spa.test.js

@@ -82,6 +82,23 @@ describe('spa', () => {
     expect(consola.log).toHaveBeenCalledWith('mounted')
     consola.log.mockClear()
   })
+
+  test('/async no asyncData leak', async () => {
+    const window = await nuxt.server.renderAndGetWindow(url('/async'))
+
+    const navigate = url => new Promise((resolve, reject) => {
+      window.$nuxt.$router.push(url, resolve, reject)
+    })
+
+    for (let i = 0; i < 3; i++) {
+      await navigate('/')
+      await navigate('/async')
+    }
+
+    const { $data } = window.$nuxt.$route.matched[0].instances.default
+    expect(Object.keys($data).length).toBe(1)
+  })
+
   // Close server and ask nuxt to stop listening to file changes
   afterAll(async () => {
     await nuxt.close()