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主要源码分析
let uid = 0 // 一个自增的id
/**
* A watcher parses an expression, collects dependencies,
* and fires callback when the expression value changes.
* This is used for both the $watch() api and directives.
*/
export default class Watcher {
vm: Component; // 组件实例
expression: string; // 表达式
cb: Function; // 回调
id: number; // 唯一标识
deep: boolean;
user: boolean;
lazy: boolean;
sync: boolean;
dirty: boolean;
active: boolean;
deps: Array<Dep>;
newDeps: Array<Dep>;
depIds: SimpleSet;
newDepIds: SimpleSet;
before: ?Function;
getter: Function;
value: any;
// 初始化各种配置
constructor (
vm: Component, // 组件实例
expOrFn: string | Function, // expression | getter
cb: Function, // 回调
options?: ?Object, // 配置信息，deep，user，lazy，sync，before
isRenderWatcher?: boolean // 是否是组件的默认watcher，使用watch时也会有watcher生成
) {
this.vm = vm
if (isRenderWatcher) {
vm._watcher = this // 设置默认watcher
}
vm._watchers.push(this) // 向组件的watcher集合中增加当前watcher
// options，配置更新，默认都是false
if (options) {
this.deep = !!options.deep
this.user = !!options.user
this.lazy = !!options.lazy
this.sync = !!options.sync
this.before = options.before
} else {
this.deep = this.user = this.lazy = this.sync = false
}
this.cb = cb // 回调函数
this.id = ++uid // uid for batching，唯一标识
this.active = true // 默认激活状态
this.dirty = this.lazy // for lazy watchers
this.deps = [] // 依赖的集合
this.newDeps = []
this.depIds = new Set()
this.newDepIds = new Set()
this.expression = process.env.NODE_ENV !== 'production'
? expOrFn.toString()
: ''
// parse expression for getter
if (typeof expOrFn === 'function') {
this.getter = expOrFn
} else {
this.getter = parsePath(expOrFn)
if (!this.getter) {
this.getter = noop
process.env.NODE_ENV !== 'production' && warn(
`Failed watching path: "${expOrFn}" ` +
'Watcher only accepts simple dot-delimited paths. ' +
'For full control, use a function instead.',
vm
)
}
}
this.value = this.lazy
? undefined
: this.get()
}
/**
* Evaluate the getter, and re-collect dependencies.
*/
get () {
pushTarget(this) // dep.js中提供的对观察者全局压栈的方法
let value
const vm = this.vm
try {
value = this.getter.call(vm, vm)
} catch (e) {
if (this.user) {
handleError(e, vm, `getter for watcher "${this.expression}"`)
} else {
throw e
}
} finally {
// "touch" every property so they are all tracked as
// dependencies for deep watching
if (this.deep) {
traverse(value) // 通过递归深层的去遍历这个对象所有的getter，实现在`src/core/obeserver/traverse.js`中。
}
popTarget() // dep.js中提供的对观察者全局出栈的方法
this.cleanupDeps() // 清空所有依赖
}
return value
}
/**
* Add a dependency to this directive.
*/
addDep (dep: Dep) {
const id = dep.id
if (!this.newDepIds.has(id)) {
this.newDepIds.add(id)
this.newDeps.push(dep)
if (!this.depIds.has(id)) {
dep.addSub(this)
}
}
}
/**
* Clean up for dependency collection.
*/
cleanupDeps () {
let i = this.deps.length
while (i--) {
const dep = this.deps[i]
if (!this.newDepIds.has(dep.id)) {
dep.removeSub(this)
}
}
let tmp = this.depIds
this.depIds = this.newDepIds
this.newDepIds = tmp
this.newDepIds.clear()
tmp = this.deps
this.deps = this.newDeps
this.newDeps = tmp
this.newDeps.length = 0
}
/**
* Subscriber interface.
* Will be called when a dependency changes.
*/
update () {
/* istanbul ignore else */
if (this.lazy) {
this.dirty = true
} else if (this.sync) {
this.run()
} else {
queueWatcher(this)
}
}
/**
* Scheduler job interface.
* Will be called by the scheduler.
*/
run () {
if (this.active) {
const value = this.get()
if (
value !== this.value ||
// Deep watchers and watchers on Object/Arrays should fire even
// when the value is the same, because the value may
// have mutated.
isObject(value) ||
this.deep
) {
// set new value
const oldValue = this.value
this.value = value
if (this.user) {
try {
this.cb.call(this.vm, value, oldValue)
} catch (e) {
handleError(e, this.vm, `callback for watcher "${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
}
}
}
let uid = 0; // 一个自增的id
/**
* A dep is an observable that can have multiple
* directives subscribing to it.
*/
export default class Dep {
static target: ?Watcher; // 用来收集依赖的观察者
id: number; // 依赖的唯一标识
subs: Array<Watcher>; // 一个观察者队列
constructor () {
this.id = uid++
this.subs = []
}
// 向观察者队列中添加一个新的订阅事件
addSub (sub: Watcher) {
this.subs.push(sub)
}
// 将观察者队列中移除一个订阅事件
removeSub (sub: Watcher) {
remove(this.subs, sub)
}
// 绑定依赖
depend () {
if (Dep.target) {
Dep.target.addDep(this)
}
}
// 更新之后通知队列里的所有订阅者
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 only one watcher
// can be evaluated at a time.
// 这一块是提供了一个全局的观察者队列的插入和取消方法
Dep.target = null
const targetStack = []
export function pushTarget (target: ?Watcher) {
targetStack.push(target)
Dep.target = target
}
export function popTarget () {
targetStack.pop()
Dep.target = targetStack[targetStack.length - 1]
}
array.js，针对数组类型，做一下hack的兼容，保证在使用数组方法的时候依然能检测到其变化，但是直接给数组对应的下标的项赋值的时候，还是检测不到的
const arrayProto = Array.prototype
export const arrayMethods = Object.create(arrayProto)
// 定义需要被劫持的方法
const methodsToPatch = [
'push',
'pop',
'shift',
'unshift',
'splice',
'sort',
'reverse'
]
/**
* Intercept mutating methods and emit events
*/
methodsToPatch.forEach(function (method) {
// cache original method
const original = arrayProto[method]
// def方法是在util文件夹下定义的，使用Object.defineProperty实现的
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)
// 通知所有订阅了这个数组变化的观察者
ob.dep.notify()
return result
})
})
scheduler.js，向外暴露了几个通用的方法。
// 重置所有的状态
function resetSchedulerState () {
index = queue.length = activatedChildren.length = 0
has = {}
if (process.env.NODE_ENV !== 'production') {
circular = {}
}
waiting = flushing = false
}
// 处理调度队列
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.
// 翻译英文就完事了
queue.sort((a, b) => a.id - b.id)
// do not cache length because more watchers might be pushed
// as we run existing watchers
// 通知到队列中所有的watcher
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
// 下面两个方法的实现见下面
callActivatedHooks(activatedQueue)
callUpdatedHooks(updatedQueue)
// devtool hook
/* istanbul ignore if */
if (devtools && config.devtools) {
devtools.emit('flush')
}
}
// 触发队列中watcher对应的组件的子组件激活activated生命周期
function callActivatedHooks (queue) {
for (let i = 0; i < queue.length; i++) {
queue[i]._inactive = true
activateChildComponent(queue[i], true /* true */)
}
}
// 触发队列中watecher对应的组件的子组件激活updated生命周期
function callUpdatedHooks (queue) {
let i = queue.length
while (i--) {
const watcher = queue[i]
const vm = watcher.vm
if (vm._watcher === watcher && vm._isMounted && !vm._isDestroyed) {
callHook(vm, 'updated')
}
}
}
/**
* 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)
}
}
}
/**
* Queue a kept-alive component that was activated during patch.
* The queue will be processed after the entire tree has been patched.
*/
// 处理keep-alive的组件
export function queueActivatedComponent (vm: Component) {
// setting _inactive to false here so that a render function can
// rely on checking whether it's in an inactive tree (e.g. router-view)
vm._inactive = false
activatedChildren.push(vm)
}
index.js，主要就是常说到的数据绑定和set方法的实现。
// 数据绑定视图，就是在get的时候收集视图依赖，在set的时候再通知已经收集的每个依赖去更新视图
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)
// vue3.0好像是用ES6的proxy重写过了
Object.defineProperty(obj, key, {
enumerable: true,
configurable: true,
get: function reactiveGetter () {
const value = getter ? getter.call(obj) : val
if (Dep.target) {
dep.depend() // 先收集依赖
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() // 通知所有依赖
}
})
}
// 动态的向组件中的对象数据插入新的属性
/**
* Set a property on an object. Adds the new property and
* triggers change notification if the property doesn't
* already exist.
*/
export function set (target: Array<any> | Object, key: any, val: any): any {
if (process.env.NODE_ENV !== 'production' &&
(isUndef(target) || isPrimitive(target))
) {
warn(`Cannot set reactive property on undefined, null, or primitive value: ${(target: any)}`)
}
// 先判断动态set的是不是数组，数组就要先改变数组长度，然后设置对应下标的值
if (Array.isArray(target) && isValidArrayIndex(key)) {
target.length = Math.max(target.length, key)
target.splice(key, 1, val) // 会触发事件通知机制，所以也可以直接返回
return val
}
// 判断这个属性是不是已经在对象中定义了，如果有也就直接赋值就可以了，因为已经绑定过视图了
if (key in target && !(key in Object.prototype)) {
target[key] = val
return val
}
const ob = (target: any).__ob__
if (target._isVue || (ob && ob.vmCount)) {
process.env.NODE_ENV !== 'production' && warn(
'Avoid adding reactive properties to a Vue instance or its root $data ' +
'at runtime - declare it upfront in the data option.'
)
return val
}
// 看它是否是已经被definereactive过了，已经添加了响应式绑定的就不再绑定了
if (!ob) {
target[key] = val
return val
}
defineReactive(ob.value, key, val) // 动态的添加响应式绑定
ob.dep.notify() // 通知所有的watcher
return val
}
// 删除对象的某一个属性，逻辑和新增类似，先处理数组，再处理对象，接着判断是否已经绑定了Obeserver，最后再动态添加响应式监听
export function del (target: Array<any> | Object, key: any) {
if (process.env.NODE_ENV !== 'production' &&
(isUndef(target) || isPrimitive(target))
) {
warn(`Cannot delete reactive property on undefined, null, or primitive value: ${(target: any)}`)
}
if (Array.isArray(target) && isValidArrayIndex(key)) {
target.splice(key, 1)
return
}
const ob = (target: any).__ob__
if (target._isVue || (ob && ob.vmCount)) {
process.env.NODE_ENV !== 'production' && warn(
'Avoid deleting properties on a Vue instance or its root $data ' +
'- just set it to null.'
)
return
}
if (!hasOwn(target, key)) {
return
}
delete target[key]
if (!ob) {
return
}
ob.dep.notify()
}
/**
* 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.
*/
// 将一个值动态的变成响应式
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
}
/**
* 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.
*/
// 暴露了一个自定义的Observer的类
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() // 可观察者对象的依赖，也就是watcher
this.vmCount = 0
// 在初始化的时候会给响应式的值绑定一个__ob__的属性，指向该实例本身
def(value, '__ob__', this)
if (Array.isArray(value)) {
if (hasProto) {
// 把hack过的数组方法复制到数组中
protoAugment(value, arrayMethods)
} else {
copyAugment(value, arrayMethods, arrayKeys)
}
this.observeArray(value) // 并且对数组中每一项进行响应式监听
} else {
this.walk(value) // 直接响应式绑定
}
}
/**
* 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])
}
}
}
小结
Vue的响应式数据的实现，就是基于自己内部实现了一整套发布-订阅模式，通过在get阶段去收集相关依赖dep，在set时去分发消息，通知所有的watcher，达到数据变化引起视图更新的效果。