feat: add and delete object attributes would trigger update.

src/utils/instance.ts

@@ -1,7 +1,7 @@
 import { ComponentInstance } from '../component'
 import vmStateManager from './vmStateManager'
 import { setCurrentInstance, getCurrentVue2Instance } from '../runtimeContext'
-import { Ref, isRef } from '../apis'
+import { Ref, isRef, isReactive } from '../apis'
 import { hasOwn, proxy, warn } from './utils'
 import { createSlotProxy, resolveSlots } from './helper'
 
@@ -20,8 +20,19 @@ export function asVmProperty(
         },
       })
     } else {
-      // @ts-ignore
-      vm[propName] = propValue
+      Object.defineProperty(vm, propName, {
+        enumerable: true,
+        configurable: true,
+        get: () => {
+          if (isReactive(propValue)) {
+            ;(propValue as any).__ob__.dep.depend()
+          }
+          return propValue
+        },
+        set: (val) => {
+          propValue = val
+        },
+      })
     }
 
     if (__DEV__) {

test/setup.spec.js

@@ -13,6 +13,8 @@ const {
   isReactive,
   defineComponent,
   onMounted,
+  set,
+  del,
 } = require('../src')
 const { sleep } = require('./helpers/utils')
 
@@ -896,6 +898,42 @@ describe('setup', () => {
     expect(vm.$el.textContent).toBe('2')
   })
 
+  // #683 #603 #580
+  it('should update directly when adding attributes to a reactive object', async () => {
+    const vm = new Vue({
+      template: '<div><button @click="add"/>{{ obj.a }}</div>',
+      setup() {
+        const obj = reactive({})
+        const add = () => {
+          set(obj, 'a', 'new property')
+        }
+        return { obj, add }
+      },
+    }).$mount()
+
+    expect(vm.$el.textContent).toBe('')
+    await vm.$el.querySelector('button').click()
+    expect(vm.$el.textContent).toBe('new property')
+  })
+
+  // #683 #603 #580
+  it('should update directly when deleting attributes from a reactive object', async () => {
+    const vm = new Vue({
+      template: '<div><button @click="deleting"/>{{ obj.a }}</div>',
+      setup() {
+        const obj = reactive({ a: 'hello' })
+        const deleting = () => {
+          del(obj, 'a')
+        }
+        return { obj, deleting }
+      },
+    }).$mount()
+
+    expect(vm.$el.textContent).toBe('hello')
+    await vm.$el.querySelector('button').click()
+    expect(vm.$el.textContent).toBe('')
+  })
+
   // #524
   it('should work with reactive arrays.', async () => {
     const opts = {