vue2.7.16源码 - Watcher

源码Watcher类型

Render Watcher

src/platforms/web/runtime/index.ts - 通过$mount绑定,后续还会在complier增强

进行$mount的挂载,调用mountComponent函数,进行元素获取

typescript 复制代码

Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  el = el && inBrowser ? query(el) : undefined
  return mountComponent(this, el, hydrating)
}

src/core/instance/lifecycle.ts - mountComponent方法

触发生命周期 beforeMount
绑定更新函数,在更新函数执行render方法,这个render方法使用的是compiler绑定的
处理存储的Watcher
触发mounted钩子

javascript 复制代码

export function mountComponent(
  vm: Component,
  el: Element | null | undefined,
  hydrating?: boolean
): Component {
  vm.$el = el
 
  callHook(vm, 'beforeMount')

  let updateComponent = () => {
      vm._update(vm._render(), hydrating)
  }
  const watcherOptions: WatcherOptions = {
    before() {
      if (vm._isMounted && !vm._isDestroyed) {
        callHook(vm, 'beforeUpdate')
      }
    }
  }
 // 创建Watcher  传入当前组件实例 和 更新方法以及配置项
  new Watcher(
    vm,   // 实例
    updateComponent, // 更新回调
    noop,   //  render Watcher用不到,是回调函数
    watcherOptions,  // 配置项
    true /* isRenderWatcher */
  )
  hydrating = false  // 重置

  // 获取预先存储的 Watcher 列表
  // 处理父组件传递的动态 props 和插槽内容
  const preWatchers = vm._preWatchers
  if (preWatchers) {
    for (let i = 0; i < preWatchers.length; i++) {
      preWatchers[i].run()
    }
  }

  // 触发mounted
  if (vm.$vnode == null) {
    vm._isMounted = true
    callHook(vm, 'mounted')
  }
  return vm
}

src/platforms/web/runtime-with-compiler.ts - compiler重写$mount

在compiler层处理render函数和目标节点,然后将这些信息传递给原始的mounted

hydrating 表示是否要复用dom节点,在patch函数中使用

typescript 复制代码

const idToTemplate = cached(id => {
  const el = query(id)
  return el && el.innerHTML
})

function getOuterHTML(el: Element): string {
  if (el.outerHTML) {
    return el.outerHTML
  } else {
    const container = document.createElement('div')
    container.appendChild(el.cloneNode(true))
    return container.innerHTML
  }
}

const mount = Vue.prototype.$mount
Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  el = el && query(el)

  // dom目标不能是body 和 html
  if (el === document.body || el === document.documentElement) {
    __DEV__ &&
      warn(
        `Do not mount Vue to <html> or <body> - mount to normal elements instead.`
      )
    return this
  }

  const options = this.$options
  
  // 第一次构建render
  if (!options.render) {
  // 获获取模板信息
    let template = options.template
    if (template) {
      if (typeof template === 'string') {
        if (template.charAt(0) === '#') {
        // 获取目标的innerHTML
          template = idToTemplate(template)
          /* istanbul ignore if */
          if (__DEV__ && !template) {
            warn(
              `Template element not found or is empty: ${options.template}`,
              this
            )
          }
        }
      } else if (template.nodeType) {
      // 如果是html节点 获取innerHTML
        template = template.innerHTML
      } else {
        if (__DEV__) {
          warn('invalid template option:' + template, this)
        }
        return this
      }
    } else if (el) {
      // 创建一个目标节点返回其html内容
      template = getOuterHTML(el)
    }
    if (template) {
   
     // 将html模板转为render函数
      const { render, staticRenderFns } = compileToFunctions(
        template,
        {
          outputSourceRange: __DEV__,
          shouldDecodeNewlines,
          shouldDecodeNewlinesForHref,
          delimiters: options.delimiters,
          comments: options.comments
        },
        this
      )
      options.render = render
      options.staticRenderFns = staticRenderFns
    }
  }
  return mount.call(this, el, hydrating)
}

Watch Watcher

src/core/instance/state.ts - initState中,触发initWatch

传入的watch数组如果是数组需要遍历创建Watcher

scss 复制代码

function initWatch(vm: Component, watch: Object) {
  for (const key in watch) {
    const handler = watch[key]
    if (isArray(handler)) {
      for (let i = 0; i < handler.length; i++) {
        createWatcher(vm, key, handler[i])
      }
    } else {
      createWatcher(vm, key, handler)
    }
  }
}

如果传入handle是一个平面对象,需要拆出handler,重新调用$watch

typescript 复制代码

function createWatcher(
  vm: Component,
  expOrFn: string | (() => any),
  handler: any,
  options?: Object
) {
  if (isPlainObject(handler)) {
    options = handler
    handler = handler.handler
  }
  if (typeof handler === 'string') {
    handler = vm[handler]
  }
  return vm.$watch(expOrFn, handler, options)
}

src/core/instance/state.ts - 绑定$watch

拆解cb中的handler
创建Watcher
如果是immediate需要先执行一边Watcher
返回Watcher清理函数

typescript 复制代码

  Vue.prototype.$watch = function (
    expOrFn: string | (() => any),
    cb: any,
    options?: Record<string, any>
  ): Function {
    // 拆解cb 会重新执行$watch
    const vm: Component = this
    if (isPlainObject(cb)) {
      return createWatcher(vm, expOrFn, cb, options)
    }
    options = options || {}
    options.user = true
    const watcher = new Watcher(vm, expOrFn, cb, options)
    if (options.immediate) {
      const info = `callback for immediate watcher "${watcher.expression}"`
      pushTarget()
      invokeWithErrorHandling(cb, vm, [watcher.value], vm, info)
      popTarget()
    }
    return function unwatchFn() {
      watcher.teardown()
    }
  }
}

Computed Watcher

src/core/instance/state.ts - initState中,触发initComputed

读取computed配置,生成Watcher
如果不存在，就调用defineComputed函数。目的是避免覆盖实例上已经存在的属性

javascript 复制代码

const computedWatcherOptions = { lazy: true }

function initComputed(vm: Component, computed: Object) {
  // 保存 _computedWatchers
  const watchers = (vm._computedWatchers = Object.create(null))
  
  const isSSR = isServerRendering()

// 遍历computed配置,按顺序生成computed Watcher
  for (const key in computed) {
    const userDef = computed[key]
    const getter = isFunction(userDef) ? userDef : userDef.get
 
    if (!isSSR) {
      // create internal watcher for the computed property.
      watchers[key] = new Watcher(
        vm,
        getter || noop,   // computed副作用函数
        noop,
        computedWatcherOptions  // 专属配置
      )
    }

    // 如果是一个新的值,要变成响应式的值
    if (!(key in vm)) {
      defineComputed(vm, key, userDef)
    } 
    }
  }
}

Watcher源码

源码地址 - src/core/observer/watcher.ts

src/v3/debug.ts - DepTarget的抽象类

typescript 复制代码

export interface DebuggerOptions {
  onTrack?: (event: DebuggerEvent) => void
  onTrigger?: (event: DebuggerEvent) => void
}

src/core/observer/dep.ts Watcher的抽象类 DepTarget

java 复制代码

export interface DepTarget extends DebuggerOptions {
  id: number
  addDep(dep: Dep): void
  update(): void
}

Watcher实现

recordEffectScope 的作用是 将副作用（Effect，如 Watcher）与当前的作用域（如组件实例）关联，实现依赖的自动清理和资源管理
根据配置判断等待执行还是立即执行getter
使用traverse深度访问响应式数据,触发深度的getter
dirty 用于实现计算属性的缓存。当依赖的响应式数据未变化时，直接返回缓存值，避免重复计算
Watcher类实现 addDep update, 提供给dep类调用

kotlin 复制代码

import {
  warn,
  remove,
  isObject,
  parsePath,
  _Set as Set,
  handleError,
  invokeWithErrorHandling,
  noop,
  isFunction
} from '../util/index'

import { traverse } from './traverse'
import { queueWatcher } from './scheduler'
import Dep, { pushTarget, popTarget, DepTarget } from './dep'
import { DebuggerEvent, DebuggerOptions } from 'v3/debug'

import type { SimpleSet } from '../util/index'
import type { Component } from 'types/component'
import { activeEffectScope, recordEffectScope } from 'v3/reactivity/effectScope'

let uid = 0

/**
 * @internal
 */
export interface WatcherOptions extends DebuggerOptions {
  deep?: boolean
  user?: boolean
  lazy?: boolean
  sync?: boolean
  before?: Function
}

/**
  *观察者解析表达式，收集依赖项，
  *并在表达式值改变时触发回调。
  *这用于$watch() api和指令。
 * @internal
 */
export default class Watcher implements DepTarget {
  vm?: Component | null
  expression: string
  cb: Function
  id: number
  deep: boolean
  user: boolean
  lazy: boolean
  sync: boolean
  dirty: boolean
  active: boolean
  deps: Array<Dep>   // 依赖数组
  newDeps: Array<Dep>  // 新的依赖数字
  depIds: SimpleSet
  newDepIds: SimpleSet
  before?: Function   // 更新前的回调
  onStop?: Function
  noRecurse?: boolean
  getter: Function
  value: any
  post: boolean

  // vue开发者使用
  onTrack?: ((event: DebuggerEvent) => void) | undefined
  onTrigger?: ((event: DebuggerEvent) => void) | undefined

  constructor(
    vm: Component | null,   //  组件实例
    expOrFn: string | (() => any),  // render Watcher的render函数
    cb: Function,                   // 回调函数
    options?: WatcherOptions | null,   // 配置
    isRenderWatcher?: boolean   //  标记是render Watcher
  ) {
    recordEffectScope(
      this,
      // if the active effect scope is manually created (not a component scope),
      // prioritize it
      activeEffectScope && !activeEffectScope._vm
        ? activeEffectScope
        : vm
        ? vm._scope
        : undefined
    )
    // 标记render目标
    if ((this.vm = vm) && isRenderWatcher) {
      vm._watcher = this
    }
    // 挂载配置项到实例
    if (options) {
      this.deep = !!options.deep
      this.user = !!options.user
      this.lazy = !!options.lazy
      this.sync = !!options.sync
      this.before = options.before
      if (__DEV__) {
        this.onTrack = options.onTrack
        this.onTrigger = options.onTrigger
      }
    } else {
        // 设置默认值
      this.deep = this.user = this.lazy = this.sync = false
    }
    this.cb = cb
    this.id = ++uid // 创建id
    this.active = true
    this.post = false
    this.dirty = this.lazy // for lazy watchers
    this.deps = []
    this.newDeps = []
    this.depIds = new Set()
    this.newDepIds = new Set()
    this.expression = __DEV__ ? expOrFn.toString() : ''
    // 获取getter的内容
    if (isFunction(expOrFn)) {
      this.getter = expOrFn
    } else {
      this.getter = parsePath(expOrFn)
      if (!this.getter) {
        this.getter = noop
        __DEV__ &&
          warn(
            `Failed watching path: "${expOrFn}" ` +
              'Watcher only accepts simple dot-delimited paths. ' +
              'For full control, use a function instead.',
            vm
          )
      }
    }
    // 延迟延迟获取 或者是 主动触发
    this.value = this.lazy ? undefined : this.get()
  }

  /**
   * 执行getter 并且重新收集依赖
   */
  get() {
    pushTarget(this)
    let value
    const vm = this.vm
    try {
      value = this.getter.call(vm, vm)
    } catch (e: any) {
      if (this.user) {
        handleError(e, vm, `getter for watcher "${this.expression}"`)
      } else {
        throw e
      }
    } finally {
      // 如果是深度监听 需要深度遍历 ,因为在前面变为响应了,需要访问一下触发一下get
      if (this.deep) {
        traverse(value)
      }
      popTarget()
      // 清空依赖 更新deps数组
      this.cleanupDeps()
    }
    return value
  }

  /**
   * 操作dep的增加
   */
  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: any = 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) {
          const info = `callback for watcher "${this.expression}"`
          invokeWithErrorHandling(
            this.cb,
            this.vm,
            [value, oldValue],
            this.vm,
            info
          )
        } 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.vm && !this.vm._isBeingDestroyed) {
      remove(this.vm._scope.effects, this)
    }
    if (this.active) {
      let i = this.deps.length
      while (i--) {
        this.deps[i].removeSub(this)
      }
      this.active = false
      if (this.onStop) {
        this.onStop()
      }
    }
  }
}