// 给一个对象定一个响应式属性
export function defineReactive (
obj: Object,
key: string,
val: any,
customSetter?: ?Function,
shallow?: boolean
) {
// dep和key 1：1
// 如果key的值变化，通知更新
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]
}
// 递归遍历
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() // dep和watcher互相添加映射关系
// 子Ob实例也要添加映射关系
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()
}
})
}
从dep.notify();开始看异步更新
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)
}
// 遍历关联所有watcher
for (let i = 0, l = subs.length; i < l; i++) {
subs[i].update()
}
}
update () {
/* istanbul ignore else */
if (this.lazy) {
this.dirty = true
} else if (this.sync) {
this.run()
} else {
// watcher入队
queueWatcher(this)
}
}
export function queueWatcher (watcher: Watcher) {
const id = watcher.id
// 去重：单个watcher只入队一次
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
if (process.env.NODE_ENV !== 'production' && !config.async) {
flushSchedulerQueue()
return
}
// 异步方式将flushSchedulerQueue放入队列
nextTick(flushSchedulerQueue)
}
}
}
问题：nextTick的作用是什么
异步方式将flushSchedulerQueue放入微任务队列
问题：nextTick怎么把flushSchedulerQueue放进去的
// 此方法就是我们平时使用的nextTick方法
export function nextTick (cb?: Function, ctx?: Object) {
let _resolve
callbacks.push(() => {
if (cb) {
try {
cb.call(ctx)
} catch (e) {
handleError(e, ctx, 'nextTick')
}
} else if (_resolve) {
_resolve(ctx)
}
})
if (!pending) {
pending = true
// 异步执行callbacks中的任务
timerFunc()
}
// $flow-disable-line
if (!cb && typeof Promise !== 'undefined') {
return new Promise(resolve => {
_resolve = resolve
})
}
}
问题：flushSchedulerQueue是怎么执行的
let timerFunc
if (typeof Promise !== 'undefined' && isNative(Promise)) {
const p = Promise.resolve()
timerFunc = () => {
p.then(flushCallbacks)
if (isIOS) setTimeout(noop)
}
isUsingMicroTask = true
} else if (!isIE && typeof MutationObserver !== 'undefined' && (
isNative(MutationObserver) ||
// PhantomJS and iOS 7.x
MutationObserver.toString() === '[object MutationObserverConstructor]'
)) {
let counter = 1
const observer = new MutationObserver(flushCallbacks)
const textNode = document.createTextNode(String(counter))
observer.observe(textNode, {
characterData: true
})
timerFunc = () => {
counter = (counter + 1) % 2
textNode.data = String(counter)
}
isUsingMicroTask = true
} else if (typeof setImmediate !== 'undefined' && isNative(setImmediate)) {
timerFunc = () => {
setImmediate(flushCallbacks)
}
} else {
// Fallback to setTimeout.
timerFunc = () => {
setTimeout(flushCallbacks, 0)
}
}
这里做了判断Promise>MutationObserver>setImmediate>setTimeout
可以看出如果真的不支持几种微任务，那就只能用setTimeout去做更新
这里执行的是p.then(flushCallbacks)并不是flushSchedulerQueue，
// 将callback中回调全部执行一遍
function flushCallbacks () {
pending = false
const copies = callbacks.slice(0)
callbacks.length = 0
for (let i = 0; i < copies.length; i++) {
copies[i]()
}
}
这里callbacks里边放的函数就是我们的flushSchedulerQueue；
function flushSchedulerQueue () {
currentFlushTimestamp = getNow()
flushing = true
let watcher, id
queue.sort((a, b) => a.id - b.id)
// 按id顺序执行watcher更新
for (index = 0; index < queue.length; index++) {
watcher = queue[index]
if (watcher.before) {
watcher.before()
}
id = watcher.id
has[id] = null
// 真正的更新函数
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')
}
}
看一下run
// watcher真正执行更新的函数
run () {
if (this.active) {
// 调用watcher的get方法
const value = this.get()
if (
value !== this.value ||
// Deep watchers and watchers on Object/Arrays should fire even
// when the value is the same, because the value may
// have mutated.
isObject(value) ||
this.deep
) {
// set new value
const oldValue = this.value
this.value = value
if (this.user) {
try {
this.cb.call(this.vm, value, oldValue)
} catch (e) {
handleError(e, this.vm, `callback for watcher "${this.expression}"`)
}
} else {
this.cb.call(this.vm, value, oldValue)
}
}
}
}
看一下watcher的get方法:其实就是updateComponent
get () {
pushTarget(this)
let value
const vm = this.vm
try {
value = this.getter.call(vm, vm)
} catch (e) {
if (this.user) {
handleError(e, vm, `getter for watcher "${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
}
get方法执行了watcher的getter
constructor (
vm: Component,
expOrFn: string | Function,
cb: Function,
options?: ?Object,
isRenderWatcher?: boolean
)
if (typeof expOrFn === 'function') {
this.getter = expOrFn
}
expOrFn就是new Watcher的时候传进来的第二个参数
new Watcher(vm, updateComponent, noop, {
before () {
if (vm._isMounted && !vm._isDestroyed) {
callHook(vm, 'beforeUpdate')
}
}
}, true /* isRenderWatcher */)
updateComponent = () => {
vm._update(vm._render(), hydrating)
}
queueWatcher先对watcher去重：
mounted() {
this.foo = Math.random()
console.log('1:' + this.foo);
this.foo = Math.random()
console.log('2:' + this.foo);
this.foo = Math.random()
console.log('3:' + this.foo);
// 异步行为，此时内容没变
console.log('p1.innerHTML:' + p1.innerHTML) // ?
// [flushCallbacks, cb1]
// callbacks: [flushScheduleQueue, cb2]
Promise.resolve().then(() => {
console.log('promise p1.innerHTML:' + p1.innerHTML)
})
// [cb, flushSchexxxx]
this.$nextTick(() => {
// 这里才是最新的值
console.log('p1.innerHTML:' + p1.innerHTML) // ?
})
}
所以只有第一次入队列
Notify()的时候回调用watcher的update，把watcher放入queueWatcher，
queueWatcher会根据ID对watcher去重，把watcher放入queue中并执行nextTick(flushSchedulerQueue)(// 异步方式将flushSchedulerQueue放入微任务队列)
这里的nextTick方法就是我们平时使用的nextTick方法，会执行timerFunc()(异步执行callbacks中的任务)
timerFunc()会调动flushCallbacks(),.对flushSchedulerQueue进行清空
flushSchedulerQueue会对queue里的watcher排序，然后挨个调用watcher.run();
run去调用watcher的get方法，const value = this.get()，get去调用传给watcher的第二个参数updateCompnent
