Observe
初始化data的時候，會調(diào)用observe(data, true),這個方法主要是初始化一個Observe的實例。
// observe data
observe(data, true /* asRootData */)
/**
* 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__ // __obo__用來記錄是否操作過observe，防止重復(fù)
} 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：
在data對象上掛載一個__ob__屬性，指向Observe實例。
每個Observe實例有一個dep屬性（Dep實例）。
Observe對vue中的每條data設(shè)置監(jiān)聽。通過以下分析可知，無論data是數(shù)組還是多層對象，observe會對data的每層屬性都設(shè)置setter和getter
/**
* Observer class that is attached to each observed
* object. Once attached, the observer converts the target
* object's property keys into getter/setters that
* collect dependencies and dispatch updates.
*/
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])
}
}
}
如果data是數(shù)組，遍歷該數(shù)組，對每條數(shù)據(jù)執(zhí)行observe方法。
/**
* Intercept mutating methods and emit events
*/
methodsToPatch.forEach(function (method) {
// cache original method
const original = arrayProto[method]
def(arrayMethods, method, function mutator (...args) {
const result = original.apply(this, args)
const ob = this.__ob__
let inserted
switch (method) {
case 'push':
case 'unshift':
inserted = args
break
case 'splice':
inserted = args.slice(2)
break
}
if (inserted) ob.observeArray(inserted)
// notify change
ob.dep.notify()
return result
})
})
在vue中，單獨處理了7個修改數(shù)組的方法（push、pop、shift、unshift、splice、sort、reverse），通過Object.defineProperty對每個方法的value進行處理，其實就是在這些方法中保留原來的用途（result），新增一些操作：拿到新增的數(shù)據(jù)inserted，對其遍歷執(zhí)行observe方法設(shè)置監(jiān)聽；這些方法中有新增、刪除、換順序，所以還需要調(diào)用ob.dep.notify()通過watcher進行更新操作。
否則遍歷data屬性，對其每個屬性通過Object.defineProperty進行數(shù)據(jù)劫持。
/**
* 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() // 依賴收集
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() // 觸發(fā)更新
}
})
}
這里是核心代碼
- 在get里面收集依賴。對屬性值val會再執(zhí)行一遍observe方法，如果是數(shù)組，遞歸處理一下。
get中判斷Dep.target:
為了區(qū)分是誰在調(diào)用data屬性的get方法，是Watcher在get（Watcher的構(gòu)造函數(shù)會調(diào)用get方法，這里會觸發(fā)defineReactive中的get），還是我們在查看賦值。如果是Watcher構(gòu)造函數(shù)觸發(fā)的，那么這個watcher就是需要收集的訂閱者。怎么判斷的呢？Dep.target初始值為null，在Watcher的get方法中，觸發(fā)defineReactive的get前會調(diào)用pushTarget方法，這里將Dep.target賦了值，觸發(fā)defineReactive的get后又調(diào)用了popTarget方法- 在set中觸發(fā)更新。
Dep
Dep是訂閱者Watcher對應(yīng)的數(shù)據(jù)依賴
- Dep.target指向Watcher。
- Dep的subs屬性用來存放多個watcher
- depend方法：Watcher收集dep
- notify：調(diào)用watcher的update方法更新數(shù)據(jù)
/**
* 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()
}
}
}
Watcher
/**
* A watcher parses an expression, collects dependencies,
* and fires callback when the expression value changes.
* This is used for both the $watch() api and directives.
*/
export default class Watcher {
vm: Component;
expression: string;
cb: Function;
id: number;
deep: boolean;
...
constructor (
vm: Component,
expOrFn: string | Function,
cb: Function,
options?: ?Object,
isRenderWatcher?: boolean
) {
this.vm = vm
if (isRenderWatcher) {
vm._watcher = this
}
vm._watchers.push(this)
...
this.value = this.lazy
? undefined
: this.get()
}
/**
* Evaluate the getter, and re-collect dependencies.
*/
get () {
pushTarget(this)
let value
const vm = this.vm
try {
value = this.getter.call(vm, vm)
} catch (e) {
if (this.user) {
handleError(e, vm, `getter for watcher "${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
}
/**
* Subscriber interface.
* Will be called when a dependency changes.
*/
update () {
/* istanbul ignore else */
if (this.lazy) {
this.dirty = true
} else if (this.sync) {
this.run()
} else {
queueWatcher(this)
}
}
/**
* Scheduler job interface.
* Will be called by the scheduler.
*/
run () {
if (this.active) {
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)
}
}
}
}
/**
* Evaluate the value of the watcher.
* This only gets called for lazy watchers.
*/
evaluate () {
this.value = this.get()
this.dirty = false
}
/**
* Depend on all deps collected by this watcher.
*/
depend () {
let i = this.deps.length
while (i--) {
this.deps[i].depend()
}
}
/**
* Remove self from all dependencies' subscriber list.
*/
teardown () {
if (this.active) {
// remove self from vm's watcher list
// this is a somewhat expensive operation so we skip it
// if the vm is being destroyed.
if (!this.vm._isBeingDestroyed) {
remove(this.vm._watchers, this)
}
let i = this.deps.length
while (i--) {
this.deps[i].removeSub(this)
}
this.active = false
}
}
}
addDep:newDepIds、newDeps中存放dep信息
update： 調(diào)用 queueWatcher
/**
* 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
if (process.env.NODE_ENV !== 'production' && !config.async) {
flushSchedulerQueue()
return
}
nextTick(flushSchedulerQueue)
}
}
}
調(diào)用：flushSchedulerQueue
/**
* Flush both queues and run the watchers.
*/
function flushSchedulerQueue () {
currentFlushTimestamp = getNow()
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')
}
}
調(diào)用watcher的run方法
掛載的時候會初始化一個Watcher實例
// we set this to vm._watcher inside the watcher's constructor
// since the watcher's initial patch may call $forceUpdate (e.g. inside child
// component's mounted hook), which relies on vm._watcher being already defined
new Watcher(vm, updateComponent, noop, {
before () {
if (vm._isMounted && !vm._isDestroyed) {
callHook(vm, 'beforeUpdate')
}
}
}, true /* isRenderWatcher */)
摘抄一段：
參考：
Vue實例化一個對象的具體過程如下：
- 新創(chuàng)建一個實例后，Vue調(diào)用compile將el轉(zhuǎn)換成vnode。
- 調(diào)用initState, 創(chuàng)建props, data的鉤子以及其對象成員的Observer（添加getter和setter）。
- 執(zhí)行mount掛載操作，在掛載時建立一個直接對應(yīng)render的Watcher，并且編譯模板生成render函數(shù)，執(zhí)行vm._update來更新DOM。
- 每當(dāng)有數(shù)據(jù)改變，都將通知相應(yīng)的Watcher執(zhí)行回調(diào)函數(shù)，更新視圖。
- 當(dāng)給這個對象的某個屬性賦值時，就會觸發(fā)set方法。
- set函數(shù)調(diào)用，觸發(fā)Dep的notify()向?qū)?yīng)的Watcher通知變化。
- Watcher調(diào)用update方法。
在這個過程中：
- Observer是用來給數(shù)據(jù)添加Dep依賴。
- Dep是data每個對象包括子對象都擁有一個該對象, 當(dāng)所綁定的數(shù)據(jù)有變更時, 通過dep.notify()通知Watcher。
- Compile是HTML指令解析器，對每個元素節(jié)點的指令進行掃描和解析，根據(jù)指令模板替換數(shù)據(jù)，以及綁定相應(yīng)的更新函數(shù)。
- Watcher是連接Observer和Compile的橋梁，Compile解析指令時會創(chuàng)建一個對應(yīng)的Watcher并綁定update方法 , 添加到Dep對象上。
