feat: add async option (#8240)

This is an option intended only for testing purposes, and should not be used in
application code.

Author: eddyerburgh

Diff for: src/core/config.js

@@ -28,6 +28,9 @@ export type Config = {
   getTagNamespace: (x?: string) => string | void;
   mustUseProp: (tag: string, type: ?string, name: string) => boolean;
 
+  // private
+  async: boolean;
+
   // legacy
   _lifecycleHooks: Array<string>;
 };
@@ -114,6 +117,12 @@ export default ({
    */
   mustUseProp: no,
 
+  /**
+   * Perform updates asynchronously. Intended to be used by Vue Test Utils
+   * This will significantly reduce performance if set to false.
+   */
+  async: true,
+
   /**
    * Exposed for legacy reasons
    */

Diff for: src/core/observer/dep.js

@@ -2,6 +2,7 @@
 
 import type Watcher from './watcher'
 import { remove } from '../util/index'
+import config from '../config'
 
 let uid = 0
 
@@ -36,6 +37,12 @@ export default class Dep {
   notify () {
     // stabilize the subscriber list first
     const subs = this.subs.slice()
+    if (process.env.NODE_ENV !== 'production' && !config.async) {
+      // subs aren't sorted in scheduler if not running async
+      // we need to sort them now to make sure they fire in correct
+      // order
+      subs.sort((a, b) => a.id - b.id)
+    }
     for (let i = 0, l = subs.length; i < l; i++) {
       subs[i].update()
     }

Diff for: src/core/observer/scheduler.js

@@ -145,6 +145,11 @@ export function queueWatcher (watcher: Watcher) {
     // queue the flush
     if (!waiting) {
       waiting = true
+
+      if (process.env.NODE_ENV !== 'production' && !config.async) {
+        flushSchedulerQueue()
+        return
+      }
       nextTick(flushSchedulerQueue)
     }
   }

Diff for: test/unit/features/global-api/config.spec.js

@@ -55,4 +55,71 @@ describe('Global config', () => {
       Vue.config.ignoredElements = []
     })
   })
+
+  describe('async', () => {
+    it('does not update synchronously when true', () => {
+      const spy = jasmine.createSpy()
+      const vm = new Vue({
+        template: `<div :class="value"></div>`,
+        updated: spy,
+        data: { value: true }
+      }).$mount()
+      vm.value = false
+      expect(spy).not.toHaveBeenCalled()
+    })
+
+    it('updates synchronously when false', () => {
+      const spy = jasmine.createSpy()
+      Vue.config.async = false
+      const vm = new Vue({
+        template: `<div :class="value"></div>`,
+        updated: spy,
+        data: { value: true }
+      }).$mount()
+      vm.value = false
+      expect(spy).toHaveBeenCalled()
+      Vue.config.async = true
+    })
+
+    it('runs watchers in correct order when false', () => {
+      Vue.config.async = false
+      const vm = new Vue({
+        template: `
+          <div id="app">
+            {{ computed }}
+          </div>`,
+        props: ['prop'],
+        propsData: {
+          'prop': []
+        },
+        data: () => ({
+          data: ''
+        }),
+        computed: {
+          computed () {
+            return this.prop.join(',')
+          }
+        },
+        watch: {
+          prop: 'execute'
+        },
+        methods: {
+          execute () {
+            this.data = this.computed
+          }
+        }
+      }).$mount()
+      expect(vm.computed).toBe('')
+      expect(vm.data).toBe('')
+
+      vm.prop = [1, 2, 3]
+      expect(vm.computed).toBe('1,2,3')
+      expect(vm.data).toBe('1,2,3')
+
+      vm.prop.push(4, 5)
+      expect(vm.computed).toBe('1,2,3,4,5')
+      expect(vm.data).toBe('1,2,3,4,5')
+      Vue.config.async = true
+    })
+  })
 })

Diff for: types/test/vue-test.ts

@@ -73,6 +73,7 @@ class Test extends Vue {
     };
     config.keyCodes = { esc: 27 };
     config.ignoredElements = ['foo', /^ion-/];
+    config.async = false
   }
 
   static testMethods() {

Diff for: types/vue.d.ts

@@ -74,6 +74,7 @@ export interface VueConfiguration {
   warnHandler(msg: string, vm: Vue, trace: string): void;
   ignoredElements: (string | RegExp)[];
   keyCodes: { [key: string]: number | number[] };
+  async: boolean;
 }
 
 export interface VueConstructor<V extends Vue = Vue> {