提到 vue 的双向数据绑定原理，我们都知道是利用了 Object.defineProperty 给数据添加 getter 和 setter，来进行依赖收集和数据派发更新，首先我们再来熟悉一下这个方法
MDN 中写到 Object.defineProperty() 方法会直接在一个对象上定义一个新属性，或者修改一个对象的现有属性， 并返回这个对象
function Person () {}
Object.defineProperty(Person.prototype, 'sayHello', {
enumerable: true,
configurable: true,
get: function () {
return `my name is ${this.name}`
},
set:function (value) {
this.name = value
}
})
let p = new Person()
p.name = 'renbo'
console.log(p.sayHello) // my name is renbo我们在实现一个极简版双向绑定
<div>请输入:</div>
<input type="text" id="input">
<div id="content"></div>
let obj = {}
Object.definePerperty(obj,'text', {
get:function () {
console.log('获得的值')
},
set:function (newVal) {
console.log('设置的值')
document.getElementById('input').value = newVal
document.getElementById('content').innerHTML = newVal;
}
})
const input = document.getElementById('input');
input.addEventListener('keyup', function(e){
obj.text = e.target.value;
})set 提供 setter 方法，当我们对 p.name 做修改的时候会触发 setter 方法， 我们访问 sayHello 的时候会触发 getter 方法，取到对应的值，那么一旦对象拥有了 getter 和 setter，就把这个对象变为自动存取的响应对象
在 vue _init 阶段我们还执行了 initState(vm) 方法，我们上篇文章写到这个方法主要是对 props、methods、data、computed 和 wathcer 等属性做了初始化操作,在 src/core/instance/state.js 中定义
export function initState (vm: Component) {
vm._watchers = []
const opts = vm.$options
if (opts.props) initProps(vm, opts.props)
if (opts.methods) initMethods(vm, opts.methods)
if (opts.data) {
initData(vm)
} else {
observe(vm._data = {}, true /* asRootData */)
}
if (opts.computed) initComputed(vm, opts.computed)
if (opts.watch && opts.watch !== nativeWatch) {
initWatch(vm, opts.watch)
}
}function initProps (vm: Component, propsOptions: Object) {
const propsData = vm.$options.propsData || {}
const props = vm._props = {}
// cache prop keys so that future props updates can iterate using Array
// instead of dynamic object key enumeration.
const keys = vm.$options._propKeys = []
const isRoot = !vm.$parent
// root instance props should be converted
if (!isRoot) {
toggleObserving(false)
}
for (const key in propsOptions) {
keys.push(key)
const value = validateProp(key, propsOptions, propsData, vm)
/* istanbul ignore else */
if (process.env.NODE_ENV !== 'production') {
const hyphenatedKey = hyphenate(key)
if (isReservedAttribute(hyphenatedKey) ||
config.isReservedAttr(hyphenatedKey)) {
warn(
`"${hyphenatedKey}" is a reserved attribute and cannot be used as component prop.`,
vm
)
}
defineReactive(props, key, value, () => {
if (!isRoot && !isUpdatingChildComponent) {
warn(
`Avoid mutating a prop directly since the value will be ` +
`overwritten whenever the parent component re-renders. ` +
`Instead, use a data or computed property based on the prop's ` +
`value. Prop being mutated: "${key}"`,
vm
)
}
})
} else {
defineReactive(props, key, value)
}
// static props are already proxied on the component's prototype
// during Vue.extend(). We only need to proxy props defined at
// instantiation here.
if (!(key in vm)) {
proxy(vm, `_props`, key)
}
}
toggleObserving(true)
}从上面代码中我们看到 props 过程，主要就是遍历 propsOptions ，调用 defineReactive 方法和 proxy，但是上面在开发环境中调用 defineReactive 给一个警告，平时我们通过 props 方法来接受父组件所传过来的值，但是这个过程是单项的，父组件可以改变传给子组件的值，但是如果子组件想改变所接受的值并传给父组件是不可以的，会收到这个警告
这个错误告诉我们避免去直接更改 props 因为当父组件重新渲染时，该值就会被覆盖。这个时候就需要用到计算属性或者侦听属性了。
defineReactive 方法和 proxy 具体作用我们在后面介绍。
function initData (vm: Component) {
let data = vm.$options.data
data = vm._data = typeof data === 'function'
? getData(data, vm)
: data || {}
if (!isPlainObject(data)) {
data = {}
process.env.NODE_ENV !== 'production' && warn(
'data functions should return an object:\n' +
'https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',
vm
)
}
// proxy data on instance
const keys = Object.keys(data)
const props = vm.$options.props
const methods = vm.$options.methods
let i = keys.length
while (i--) {
const key = keys[i]
if (process.env.NODE_ENV !== 'production') {
if (methods && hasOwn(methods, key)) {
warn(
`Method "${key}" has already been defined as a data property.`,
vm
)
}
}
if (props && hasOwn(props, key)) {
process.env.NODE_ENV !== 'production' && warn(
`The data property "${key}" is already declared as a prop. ` +
`Use prop default value instead.`,
vm
)
} else if (!isReserved(key)) {
proxy(vm, `_data`, key)
}
}
// observe data
observe(data, true /* asRootData */)
}initData 主要是遍历data，取到对应的key 调用 proxy ；另一个是调用 observe 方法
平时我们写 vue 的时候我们可以直接在方法中访问 props 和 data，看下面例子
props: {
name: {
type: String,
default () {
return 'renbo'
}
}
},
data:{
return {
age: 26
}
},
methods: {
sayHello () {
console.log(this.name, this.age)
}
}这就是通过 proxy 将 props 和 data 上的属性代理到 vm 实例上，所以我们可以直接通过 this 访问到
那么我们看看 proxy 是如何定义的呢
export function proxy (target: Object, sourceKey: string, key: string) {
sharedPropertyDefinition.get = function proxyGetter () {
return this[sourceKey][key]
}
sharedPropertyDefinition.set = function proxySetter (val) {
this[sourceKey][key] = val
}
Object.defineProperty(target, key, sharedPropertyDefinition)
}通过 Object.defineProperty 把 target[sourceKey][key] 的读写变成了对 target[key] 的读写，所以对于 props 和 data 而言就是
vm._props.xxx -> vm.xxx
vm._data.xxx -> vm.xxx上面在 initData中调用了 observe 函数，进入文件 src/core/observer/index.js 中
**
* Attempt to create an observer instance for a value,
* returns the new observer if successfully observed,
* or the existing observer if the value already has one.
*/
export function observe (value: any, asRootData: ?boolean): Observer | void {
if (!isObject(value) || value instanceof VNode) {
return
}
let ob: Observer | void
if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
ob = value.__ob__
} else if (
shouldObserve &&
!isServerRendering() &&
(Array.isArray(value) || isPlainObject(value)) &&
Object.isExtensible(value) &&
!value._isVue
) {
ob = new Observer(value)
}
if (asRootData && ob) {
ob.vmCount++
}
return ob
}observe 就是给除了 vnode 的对象类型的数据添加一个观察者实例
如果已经添加过则直接返回，否则在满足一定条件下去 new Observer
接下来我们来看一下 Observer 的作用
export class Observer {
value: any;
dep: Dep;
vmCount: number; // number of vms that have this object as root $data
constructor (value: any) {
this.value = value
this.dep = new Dep()
this.vmCount = 0
def(value, '__ob__', this)
if (Array.isArray(value)) {
if (hasProto) {
protoAugment(value, arrayMethods)
} else {
copyAugment(value, arrayMethods, arrayKeys)
}
this.observeArray(value)
} else {
this.walk(value)
}
}
/**
* Walk through all properties and convert them into
* getter/setters. This method should only be called when
* value type is Object.
*/
walk (obj: Object) {
const keys = Object.keys(obj)
for (let i = 0; i < keys.length; i++) {
defineReactive(obj, keys[i])
}
}
/**
* Observe a list of Array items.
*/
observeArray (items: Array<any>) {
for (let i = 0, l = items.length; i < l; i++) {
observe(items[i])
}
}
}Observer 是一个构造函数
- 在constructor 中实例化了 Dep 对象
- 执行了
def(value, '__ob__', this) - 对 value 进行判断，如果是数组调用 observeArray，如果是纯对象调用 walk
- observeArray 方法中遍历数组再次调用 observer，而 walk 遍历对象的 key 调用 defineReactive
Dep 主要的作用就是进行依赖收集，是整个 getter 的核心，在后面会介绍，def 函数是通过 Object.defineProperty 的封装的，作用是将自身实例添加到数据对象 value 的 __ob__ 属性上，这样我们在开发中就会看到 data 上对象类型的数据多了一个 __ob__ 的属性
defineReactive 的作用就是定义一个响应式对象，给对象动态添加 getter 和 setter
/**
* Define a reactive property on an Object.
*/
export function defineReactive (
obj: Object,
key: string,
val: any,
customSetter?: ?Function,
shallow?: boolean
) {
const dep = new Dep()
const property = Object.getOwnPropertyDescriptor(obj, key)
if (property && property.configurable === false) {
return
}
// cater for pre-defined getter/setters
const getter = property && property.get
const setter = property && property.set
if ((!getter || setter) && arguments.length === 2) {
val = obj[key]
}
let childOb = !shallow && observe(val)
Object.defineProperty(obj, key, {
enumerable: true,
configurable: true,
get: function reactiveGetter () {
const value = getter ? getter.call(obj) : val
if (Dep.target) {
dep.depend()
if (childOb) {
childOb.dep.depend()
if (Array.isArray(value)) {
dependArray(value)
}
}
}
return value
},
set: function reactiveSetter (newVal) {
const value = getter ? getter.call(obj) : val
/* eslint-disable no-self-compare */
if (newVal === value || (newVal !== newVal && value !== value)) {
return
}
/* eslint-enable no-self-compare */
if (process.env.NODE_ENV !== 'production' && customSetter) {
customSetter()
}
// #7981: for accessor properties without setter
if (getter && !setter) return
if (setter) {
setter.call(obj, newVal)
} else {
val = newVal
}
childOb = !shallow && observe(newVal)
dep.notify()
}
})
}defineReactive 函数
- new Dep()
- 通过 Object.getOwnPropertyDescriptor 拿到 obj 的属性描述符
- 对子对象递归调用 observe 方法，把所有子属性变成响应式对象
- 利用 Object.defineProperty 给 obj 的属性 key 添加 getter 和 setter
下面我们通过上面的逻辑步骤整理下面一张图
通过上面的逻辑和总结发现响应式对象的核心其实就是利用 Object.defineProperty 给数据添加了 getter 和 setter，来进行依赖收集dep.depend() 和派发更新 dep.notify()
通过响应式对象我们知道在 defineReactive 函数内的 Object.defineProperty 定义的 get 内部实例了 Dep
const dep = new Dep()
dep.depend()前文说过 Dep 是整个 getter 依赖收集的核心，打开文件在 src/core/observer/dep.js
// ...
/**
* A dep is an observable that can have multiple
* directives subscribing to it.
*/
export default class Dep {
static target: ?Watcher;
id: number;
subs: Array<Watcher>;
constructor () {
this.id = uid++
this.subs = []
}
addSub (sub: Watcher) {
this.subs.push(sub)
}
removeSub (sub: Watcher) {
remove(this.subs, sub)
}
depend () {
if (Dep.target) {
Dep.target.addDep(this)
}
}
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()
}
}
}
// the current target watcher being evaluated.
// this is globally unique because there could be only one
// watcher being evaluated at any time.
Dep.target = null
const targetStack = []
export function pushTarget (_target: ?Watcher) {
if (Dep.target) targetStack.push(Dep.target)
Dep.target = _target
}
export function popTarget () {
Dep.target = targetStack.pop()
}我们来看一下 Dep 中主要就是对 Watcher 的一种管理，其中 subs: Array<Watcher>; 就是订阅者列表,在Watcher 中进行定义
查看 src/core/observer/watcher.js
let uid = 0
/**
* A watcher parses an expression, collects dependencies,
* and fires callback when the expression value changes.
* This is used for both the $watch() api and directives.
*/
export default class Watcher {
vm: Component;
expression: string;
cb: Function;
id: number;
deep: boolean;
user: boolean;
computed: boolean;
sync: boolean;
dirty: boolean;
active: boolean;
dep: Dep;
deps: Array<Dep>;
newDeps: Array<Dep>;
depIds: SimpleSet;
newDepIds: SimpleSet;
before: ?Function;
getter: Function;
value: any;
constructor (
vm: Component,
expOrFn: string | Function,
cb: Function,
options?: ?Object,
isRenderWatcher?: boolean
) {
this.vm = vm
if (isRenderWatcher) {
vm._watcher = this
}
vm._watchers.push(this)
// options
if (options) {
this.deep = !!options.deep
this.user = !!options.user
this.computed = !!options.computed
this.sync = !!options.sync
this.before = options.before
} else {
this.deep = this.user = this.computed = this.sync = false
}
this.cb = cb
this.id = ++uid // uid for batching
this.active = true
this.dirty = this.computed // for computed watchers
this.deps = []
this.newDeps = []
this.depIds = new Set()
this.newDepIds = new Set()
this.expression = process.env.NODE_ENV !== 'production'
? expOrFn.toString()
: ''
// parse expression for getter
if (typeof expOrFn === 'function') {
this.getter = expOrFn
} else {
this.getter = parsePath(expOrFn)
if (!this.getter) {
this.getter = function () {}
process.env.NODE_ENV !== 'production' && warn(
`Failed watching path: "${expOrFn}" ` +
'Watcher only accepts simple dot-delimited paths. ' +
'For full control, use a function instead.',
vm
)
}
}
if (this.computed) {
this.value = undefined
this.dep = new Dep()
} else {
this.value = this.get()
}
}
/**
* Evaluate the getter, and re-collect dependencies.
*/
get () {
pushTarget(this)
let value
const vm = this.vm
try {
value = this.getter.call(vm, vm)
} catch (e) {
if (this.user) {
handleError(e, vm, `getter for watcher "${this.expression}"`)
} else {
throw e
}
} finally {
// "touch" every property so they are all tracked as
// dependencies for deep watching
if (this.deep) {
traverse(value)
}
popTarget()
this.cleanupDeps()
}
return value
}
/**
* Add a dependency to this directive.
*/
addDep (dep: Dep) {
const id = dep.id
if (!this.newDepIds.has(id)) {
this.newDepIds.add(id)
this.newDeps.push(dep)
if (!this.depIds.has(id)) {
dep.addSub(this)
}
}
}
/**
* Clean up for dependency collection.
*/
cleanupDeps () {
let i = this.deps.length
while (i--) {
const dep = this.deps[i]
if (!this.newDepIds.has(dep.id)) {
dep.removeSub(this)
}
}
let tmp = this.depIds
this.depIds = this.newDepIds
this.newDepIds = tmp
this.newDepIds.clear()
tmp = this.deps
this.deps = this.newDeps
this.newDeps = tmp
this.newDeps.length = 0
}
// ...
}当我们在 mount 过程中调用 mountComponent 函数的时候实例化了 new Watcher, 然后执行了 this.get() 方法
进入 get 函数 会执行 pushTarget(this)
打开文件 src/core/observer/dep.js
export function pushTarget (target: ?Watcher) {
targetStack.push(target)
Dep.target = target
}pushTarget 主要两个作用
- 把 Dep.target 赋值为当前的 Watcher
- 将 target 进行压栈操作
接着执行
value = this.getter.call(vm, vm)this.getter 对应就是 updateComponent 函数，这实际上就是在执行：
vm._update(vm._render(), hydrating)它会先执行 vm._render() 方法，生成渲染 VNode，访问 vm 上的数据，这样就触发了数据对象的 getter。 每个getter 上都有一个 dep ，这样就是调用 dep.depend() 进行依赖收集
addDep (dep: Dep) {
const id = dep.id
if (!this.newDepIds.has(id)) {
this.newDepIds.add(id)
this.newDeps.push(dep)
if (!this.depIds.has(id)) {
dep.addSub(this)
}
}
}在保证添加的数据的唯一性 后执行 dep.addSub(this)
也就是执行了this.subs.push(sub)
通过上面的执行顺序，当前的 watcher 已经订阅到了数据 dep 的 subs 数组中，当数据放生改变在进行 dep.notify
接下来执行递归去访问 value，触发它所有子项的 getter
if (this.deep) {
traverse(value)
}之后执行 popTarget(),打开文件 src/core/observer/dep.js
export function popTarget () {
targetStack.pop()
Dep.target = targetStack[targetStack.length - 1]
}这个时候 vm 的数据依赖收集已经完成需要将 Dep.target 改变成上一个状态，完成 Dep.target 渲染，最后执行this.cleanupDeps() 进行依赖清空
cleanupDeps () {
let i = this.deps.length
while (i--) {
const dep = this.deps[i]
if (!this.newDepIds.has(dep.id)) {
dep.removeSub(this)
}
}
let tmp = this.depIds
this.depIds = this.newDepIds
this.newDepIds = tmp
this.newDepIds.clear()
tmp = this.deps
this.deps = this.newDeps
this.newDeps = tmp
this.newDeps.length = 0
}在执行 cleanupDeps 函数，首先遍历 deps，移除对 dep.subs 数组中 Wathcer 的订阅，把 newDepIds 和 depIds 交换，newDeps 和 deps 交换，并把 newDepIds 和 newDeps 清空，因为 newDeps 是新添加的 Dep 实例数组，而 deps 表示上一次添加的 Dep 实例数组，所以每次订阅，在subs 中都是最新的，这样就完成了整个依赖收集
通过 sub 这个数组，当我们修改数据的时候，就可以更新 sub 数组 进行派发更新，下面在进行代码分析这个过程
通过 defineReactive 函数中，定义响应式的 setter 调用了 dep.notify() 来通知所有订阅者，我们要更新了。
export function defineReactive (
obj: Object,
key: string,
val: any,
customSetter?: ?Function,
shallow?: boolean
) {
const dep = new Dep()
const property = Object.getOwnPropertyDescriptor(obj, key)
if (property && property.configurable === false) {
return
}
// cater for pre-defined getter/setters
const getter = property && property.get
const setter = property && property.set
if ((!getter || setter) && arguments.length === 2) {
val = obj[key]
}
let childOb = !shallow && observe(val)
Object.defineProperty(obj, key, {
enumerable: true,
configurable: true,
// ...
set: function reactiveSetter (newVal) {
const value = getter ? getter.call(obj) : val
/* eslint-disable no-self-compare */
if (newVal === value || (newVal !== newVal && value !== value)) {
return
}
/* eslint-enable no-self-compare */
if (process.env.NODE_ENV !== 'production' && customSetter) {
customSetter()
}
if (setter) {
setter.call(obj, newVal)
} else {
val = newVal
}
childOb = !shallow && observe(newVal)
dep.notify()
}
})
}当我们修改了数据，触发了 setter ，调用 dep.notify() ,遍历所有 subs，调用 watcher 的 update 方法
// src/core/observer/dep.js
class Dep {
// ...
notify () {
// stabilize the subscriber list first
const subs = this.subs.slice()
for (let i = 0, l = subs.length; i < l; i++) {
subs[i].update()
}
}
}// src/core/observer/watcher.js
class Watcher {
// ...
update () {
/* istanbul ignore else */
if (this.computed) {
// A computed property watcher has two modes: lazy and activated.
// It initializes as lazy by default, and only becomes activated when
// it is depended on by at least one subscriber, which is typically
// another computed property or a component's render function.
if (this.dep.subs.length === 0) {
// In lazy mode, we don't want to perform computations until necessary,
// so we simply mark the watcher as dirty. The actual computation is
// performed just-in-time in this.evaluate() when the computed property
// is accessed.
this.dirty = true
} else {
// In activated mode, we want to proactively perform the computation
// but only notify our subscribers when the value has indeed changed.
this.getAndInvoke(() => {
this.dep.notify()
})
}
} else if (this.sync) {
this.run()
} else {
queueWatcher(this)
}
}
} 在进行 update 的时候会根据不同场景去派发更新，computed 与 sync 我们放在后面来说，这两个状态也就是我们的计算属性（computed）和侦听属性（watch），先看一下 queueWatcher
// src/core/observer/scheduler.js
const queue: Array<Watcher> = []
let has: { [key: number]: ?true } = {}
let waiting = false
let flushing = false
/**
* Push a watcher into the watcher queue.
* Jobs with duplicate IDs will be skipped unless it's
* pushed when the queue is being flushed.
*/
export function queueWatcher (watcher: Watcher) {
const id = watcher.id
if (has[id] == null) {
has[id] = true
if (!flushing) {
queue.push(watcher)
} else {
// if already flushing, splice the watcher based on its id
// if already past its id, it will be run next immediately.
let i = queue.length - 1
while (i > index && queue[i].id > watcher.id) {
i--
}
queue.splice(i + 1, 0, watcher)
}
// queue the flush
if (!waiting) {
waiting = true
nextTick(flushSchedulerQueue)
}
}
}用 has 保证在同一个 watcher 只添加一次，并且在派发更新的时候每次数据改变并不会都触发� watcher ，而是把watcher添加到队列里面通过执行 nextTick，下面来看一下 flushSchedulerQueue
// src/core/observer/scheduler.js
let flushing = false
let index = 0
/**
* Flush both queues and run the watchers.
*/
function flushSchedulerQueue () {
flushing = true
let watcher, id
// Sort queue before flush.
// This ensures that:
// 1. Components are updated from parent to child. (because parent is always
// created before the child)
// 2. A component's user watchers are run before its render watcher (because
// user watchers are created before the render watcher)
// 3. If a component is destroyed during a parent component's watcher run,
// its watchers can be skipped.
queue.sort((a, b) => a.id - b.id)
// do not cache length because more watchers might be pushed
// as we run existing watchers
for (index = 0; index < queue.length; index++) {
watcher = queue[index]
if (watcher.before) {
watcher.before()
}
id = watcher.id
has[id] = null
watcher.run()
// in dev build, check and stop circular updates.
if (process.env.NODE_ENV !== 'production' && has[id] != null) {
circular[id] = (circular[id] || 0) + 1
if (circular[id] > MAX_UPDATE_COUNT) {
warn(
'You may have an infinite update loop ' + (
watcher.user
? `in watcher with expression "${watcher.expression}"`
: `in a component render function.`
),
watcher.vm
)
break
}
}
}
// keep copies of post queues before resetting state
const activatedQueue = activatedChildren.slice()
const updatedQueue = queue.slice()
resetSchedulerState()
// call component updated and activated hooks
callActivatedHooks(activatedQueue)
callUpdatedHooks(updatedQueue)
// devtool hook
/* istanbul ignore if */
if (devtools && config.devtools) {
devtools.emit('flush')
}
}首先执行对队列做了从小到大的排序
-
组件的更新由父到子；因为父组件的创建过程是先于子的，所以 watcher 的创建也是先父后子，执行顺序也应该保持先父后子。
-
用户的自定义 watcher 要优先于渲染 watcher 执行；因为用户自定义 watcher 是在渲染 watcher 之前创建的。
-
如果一个组件在父组件的 watcher 执行期间被销毁，那么它对应的 watcher 执行都可以被跳过，所以父组件的 watcher 应该先执行。
其次进行队列遍历
拿到对应的 watcher，执行 watcher.run()。如果在遍历的时候，用户有再添加新的 watcher 动作， 那么就在队列中从后往前找，找到第一个没有插入的 watcher 的 id 比当前队列中 watcher 的 id 的大的位置，放到队列中
export function queueWatcher (watcher: Watcher) {
const id = watcher.id
if (has[id] == null) {
has[id] = true
if (!flushing) {
queue.push(watcher)
} else {
// if already flushing, splice the watcher based on its id
// if already past its id, it will be run next immediately.
let i = queue.length - 1
while (i > index && queue[i].id > watcher.id) {
i--
}
queue.splice(i + 1, 0, watcher)
}
// ...
}
}这样在执行 watcher.run() 时候，通过 this.get() 就能得到 watcher 当前的值，然后通过判断 新旧值不等、新值是对象类型、deep 模式中的任何一个条件成立都会触发 watcher 回调，传入新的 value 和 旧的 value，这样我们在我们自定义 watcher 的时候就可以在回调函数中拿到两个值。
当我们数据发生改变的时候，触发setter ，因为 watcher 是一个队列，通过调度进行了优化 在 nextTick 后执行所有 watcher 的 run 然后触发所有 watcher 的 update 进行进行 patch
通过上面几个模块的分析我们基本知道了 vue 的响应式过程，在生成响应对象的时候需要注意的是，vue 更新对象数组必须用他的全局方法也就是 vue.set,vue.get,vue.del 等，否则是不会触发setter，导致视图更新失败。