fix(reactivity): track length on for in iteration on Array

fix #2427

packages/reactivity/__tests__/reactiveArray.spec.ts

@@ -128,6 +128,21 @@ describe('reactivity/reactive/Array', () => {
  expect(fn).toHaveBeenCalledTimes(1)
  })
 
+ // #2427
+ test('track length on for ... in iteration', () => {
+ const array = reactive([1])
+ let length = ''
+ effect(() => {
+ length = ''
+ for (const key in array) {
+ length += key
+ }
+ })
+ expect(length).toBe('0')
+ array.push(1)
+ expect(length).toBe('01')
+ })
+
  describe('Array methods w/ refs', () => {
  let original: any[]
  beforeEach(() => {

packages/reactivity/src/baseHandlers.ts

@@ -179,7 +179,7 @@ function has(target: object, key: string | symbol): boolean {
 }
 
 function ownKeys(target: object): (string | number | symbol)[] {
- track(target, TrackOpTypes.ITERATE, ITERATE_KEY)
+ track(target, TrackOpTypes.ITERATE, isArray(target) ? 'length' : ITERATE_KEY)
  return Reflect.ownKeys(target)
 }