Vue3.0 响应式系统源码逐行分析讲解

来源：jb51　　时间：2019/10/14 12:24:12　　对本文有异议

前言

关于响应式原理想必大家都很清楚了，下面我将会根据响应式API来具体讲解Vue3.0中的实现原理, 另外我只会针对get,set进行深入分析，本文包含以下API实现，推荐大家顺序阅读

effect
reactive
readonly
computed
ref

对了，大家一定要先知道怎么用哦~

引子

先来段代码，大家可以直接复制哦，注意引用的文件

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <meta http-equiv="X-UA-Compatible" content="ie=edge">
 <title>Document</title>
 <script src="../packages/vue/dist/vue.global.js"></script>
</head>
<body>
 <div id="app"></div>
 <script>
  const { reactive, computed, effect, watch, createApp } = Vue
  const App = {
   template: `
    <div id="box">
      <button @click="increment">{{ state.count }}</button>
    </div> 
   `,
   setup() {
    const state = reactive({
     count: 0
    })
    function increment(e) {
     state.count++
    }
    effect(() => {
     console.log('count改变', state.count);
    })
    return {
     state,
     increment
    }
   }
  }
  createApp().mount(App, '#app')
 </script>
</body>
</html>

这段代码，想必大家都看得懂，点击后count增加，视图也随之更新，effect监听了count改变，那么为什么effect能观察到count变化呢,还有为什么reactive可以实现响应式？

effect

为什么要先说这个函数呢，因为它和其他函数都息息相关，只有先了解它才能更好的理解其他响应式API

上源码

export function effect(
 fn: Function,
 options: ReactiveEffectOptions = EMPTY_OBJ
): ReactiveEffect {
 if ((fn as ReactiveEffect).isEffect) {
  fn = (fn as ReactiveEffect).raw
 }
 const effect = createReactiveEffect(fn, options)
 if (!options.lazy) {
  effect()
 }
 return effect
}

if判断，判断如果传入的fn函数，它已经是effect了，也就是一个标识，直接获取该函数上的raw属性，这个属性后面会讲到

调用createReactiveEffect

如果options中有lazy,就会立即调用effect,其实本质上调用的还是传入的fn函数

// 了解一下options有哪些
{
 lazy?: boolean // 是否立即调用fn
 computed?: boolean // 是否是computed
 scheduler?: (run: Function) => void // 在调用fn之前执行
 onTrack?: (event: DebuggerEvent) => void // 在依赖收集完成之后调用
 onTrigger?: (event: DebuggerEvent) => void // 在调用fn之前执行，源码上来看和scheduler调用时机一样，只是传入参数不同
 onStop?: () => void // 清除依赖完成后调用
}

返回effect

createReactiveEffect

上面提到了createReactiveEffect函数，我们来看看它的实现

function createReactiveEffect(
 fn: Function,
 options: ReactiveEffectOptions
): ReactiveEffect {
 // 又包装了一层函数
 const effect = function effect(...args): any {
  return run(effect as ReactiveEffect, fn, args)
 } as ReactiveEffect
 effect.isEffect = true // 标识effect
 effect.active = true // 如果active
 effect.raw = fn // 传入的回调
 effect.scheduler = options.scheduler
 effect.onTrack = options.onTrack
 effect.onTrigger = options.onTrigger
 effect.onStop = options.onStop
 effect.computed = options.computed
 effect.deps = [] // 用于收集依赖
 return effect
}

注意，敲黑板，这里有个run函数，很重要，因为它保存了依赖

function run(effect: ReactiveEffect, fn: Function, args: any[]): any {
 if (!effect.active) {
  return fn(...args)
 }
 if (activeReactiveEffectStack.indexOf(effect) === -1) {
  cleanup(effect)
  try {
   activeReactiveEffectStack.push(effect)
   return fn(...args)
  } finally {
   activeReactiveEffectStack.pop()
  }
 }
}

他把依赖存储在了一个全局的数组中activeReactiveEffectStack, 他以栈的形式存储，调用完依赖后，会弹出，大家要留意一下这里，后面会用到

怎么样，是不是很简单~

reactive

export function reactive(target: object) {
 // 如果target是已经被readonly对象，那么直接返回对应的proxy对象
 if (readonlyToRaw.has(target)) {
  return target
 }
 
 // 如果target是已经被readonly对象，那么直接返回对应的真实对象
 if (readonlyValues.has(target)) {
  return readonly(target)
 }
 return createReactiveObject(
  target,
  rawToReactive,
  reactiveToRaw,
  mutableHandlers,
  mutableCollectionHandlers
 )
}

前两个if是用来处理这种情况的

// 情况一
const state1 = readonly({ count: 0 })
const state2 = reactive(state1)
 
// 情况二
const obj = { count: 0 }
const state1 = readonly(obj)
const state2 = reactive(obj)
可以看到reactive它的参数是被readonly的对象，reactive不会对它再次创建响应式，而是通过Map映射，拿到对应的对象，即Proxy <==> Object的相互转换。
 
 
createReactiveObject创建响应式对象,注意它的参数
createReactiveObject(
  target,
  rawToReactive,  // Object ==> Proxy
  reactiveToRaw,  // Proxy ==> Object
  mutableHandlers, // get set has ...
  mutableCollectionHandlers // 很少会用，不讲了~
)

以上就是reative一开始所做的一些事情,下面继续分析createReactiveObject

createReactiveObject

function createReactiveObject(
 target: any,
 toProxy: WeakMap<any, any>,
 toRaw: WeakMap<any, any>,
 baseHandlers: ProxyHandler<any>,
 collectionHandlers: ProxyHandler<any>
) {
 // 如果不是对象，在开发环境报出警告
 if (!isObject(target)) {
  if (__DEV__) {
   console.warn(`value cannot be made reactive: ${String(target)}`)
  }
  return target
 }
 
 let observed = toProxy.get(target)
 // 如果目标对象已经有proxy对象，直接返回
 if (observed !== void 0) {
  return observed
 }
 
 // 如果目标对象是proxy的对象，并且有对应的真实对象，那么也直接返回
 if (toRaw.has(target)) {
  return target
 }
 // 如果它是vnode或者vue，则不能被观测
 if (!canObserve(target)) {
  return target
 }
 // 判断被观测的对象是否是set,weakSet,map,weakMap,根据情况使用对应proxy的，配置对象
 const handlers = collectionTypes.has(target.constructor)
  ? collectionHandlers
  : baseHandlers
 observed = new Proxy(target, handlers)
 toProxy.set(target, observed)
 toRaw.set(observed, target)
 if (!targetMap.has(target)) {
  targetMap.set(target, new Map())
 }
 return observed
}

第一个if,判断是否是对象，否则报出警告

toProxy拿到观测对象的Proxy对象，如果存在直接返回

// 这种情况
const obj = { count: 0 }
const state1 = reative(obj)
const state2 = reative(obj)

toRaw拿到Proxy对象对应的真实对象,如果存在直接返回

// 这种情况
const obj = { count: 0 }
const state1 = reative(obj)
const state2 = reative(state1)

有些情况无法被观测,则直接返回观测对象本身

const canObserve = (value: any): boolean => {
 return (
  !value._isVue &&
  !value._isVNode &&
  observableValueRE.test(toTypeString(value)) &&
  !nonReactiveValues.has(value)
 )
}

设置handlers，即get,set等属性访问器，注意：collectionHandlers是用来处理观测对象为Set,Map等情况，很少见，这里就不讲了

 const handlers = collectionTypes.has(target.constructor)
  ? collectionHandlers
  : baseHandlers

然后创建了Proxy对象，并把观测对象和Proxy对象，分别做映射

 observed = new Proxy(target, handlers)
 toProxy.set(target, observed)
 toRaw.set(observed, target)

然后在targetMap做了target ==> Map的映射，这又是干嘛，注意：targetMap是全局的

export const targetMap: WeakMap<any, KeyToDepMap> = new WeakMap()
 if (!targetMap.has(target)) {
  targetMap.set(target, new Map())
 }

在这里先给大家卖个关子，targetMap非常重要，是用来保存依赖的地方

讲完了reactive，可以回到一开始的引子

依赖收集

说到依赖收集，不得不提到，依赖的创建，那么Vue3.0是在哪里创建了渲染依赖呢，大家可以找到下面这段代码以及文件

// vue-next\packages\runtime-core\src\createRenderer.ts
 function setupRenderEffect(
  instance: ComponentInternalInstance,
  parentSuspense: HostSuspsenseBoundary | null,
  initialVNode: HostVNode,
  container: HostElement,
  anchor: HostNode | null,
  isSVG: boolean
 ) {
  // create reactive effect for rendering
  let mounted = false
  instance.update = effect(function componentEffect() {
 // ...
  }, __DEV__ ? createDevEffectOptions(instance) : prodEffectOptions)
 }

代码特别长，我剪掉了中间部分，大家还记得effect有个选项lazy吗，没错，它默认是false，也就会立即调用传入的componentEffect回调,在它内部调用了patch实现了组件的挂载。

敲黑板，关键来了，还记得effect调用，内部会调用run方法吗

function run(effect: ReactiveEffect, fn: Function, args: any[]): any {
 if (!effect.active) {
  return fn(...args)
 }
 if (activeReactiveEffectStack.indexOf(effect) === -1) {
  cleanup(effect)
  try {
   activeReactiveEffectStack.push(effect)
   return fn(...args)
  } finally {
   activeReactiveEffectStack.pop()
  }
 }
}

这里进行了第一步的依赖收集，保存在全局数组中，为了方便触发get的对象，将依赖收集到自己的deps中
然后就是调用patch，进行组件挂载

if (!mounted) {
  const subTree = (instance.subTree = renderComponentRoot(instance))
  // beforeMount hook
  if (instance.bm !== null) {
    invokeHooks(instance.bm)
  }
  patch(null, subTree, container, anchor, instance, parentSuspense, isSVG)
  initialVNode.el = subTree.el
  // mounted hook
  if (instance.m !== null) {
    queuePostRenderEffect(instance.m, parentSuspense)
  }
  mounted = true
}

至于它内部实现，我就不讲了,不是本文重点，然后我们去编译的地方看看

//vue-next\packages\runtime-core\src\component.ts
function finishComponentSetup(
 instance: ComponentInternalInstance,
 parentSuspense: SuspenseBoundary | null
) {
 const Component = instance.type as ComponentOptions
 if (!instance.render) {
  if (Component.template && !Component.render) {
   if (compile) {
    Component.render = compile(Component.template, {
     onError(err) {}
    })
   } else if (__DEV__) {
    warn(
     `Component provides template but the build of Vue you are running ` +
      `does not support on-the-fly template compilation. Either use the ` +
      `full build or pre-compile the template using Vue CLI.`
    )
   }
  }
  if (__DEV__ && !Component.render) {
   warn(
    `Component is missing render function. Either provide a template or ` +
     `return a render function from setup().`
   )
  }
  instance.render = (Component.render || NOOP) as RenderFunction
 }
 
 // ...其他
}

上面的代码是编译部分，我们来看看例子中编译后是什么样

(function anonymous(
) {
const _Vue = Vue
const _createVNode = Vue.createVNode
 
const _hoisted_1 = { id: "box" }
 
return function render() {
 with (this) {
  const { toString: _toString, createVNode: _createVNode, openBlock: _openBlock, createBlock: _createBlock } = _Vue
  
  return (_openBlock(), _createBlock("div", _hoisted_1, [
   _createVNode("button", { onClick: increment }, _toString(state.count), 9 /* TEXT, PROPS */, ["onClick"])
  ]))
 }
}
})

可以看到，编译的代码中，有使用到state.count,那么就会触发get访问器，从而收集依赖，至于为什么能直接访问到属性，原因是由于with设置了上下文，下面我们具体分析get

get

// vue-next\packages\reactivity\src\baseHandlers.ts
function createGetter(isReadonly: boolean) {
 return function get(target: any, key: string | symbol, receiver: any) {
  const res = Reflect.get(target, key, receiver)
  if (typeof key === 'symbol' && builtInSymbols.has(key)) {
   return res
  }
  // _isRef
  if (isRef(res)) {
   return res.value
  }
  track(target, OperationTypes.GET, key)
  // 如果该属性对应的值还是对象，就继续递归创建响应式
  return isObject(res)
   ? isReadonly
    ? // need to lazy access readonly and reactive here to avoid
     // circular dependency
     readonly(res)
    : reactive(res)
   : res
 }
}

调用Reflect.get获取属性值

如果key是symbol并且是Symbol的一个属性，就直接返回该值

// 这种情况
const key = Symbol('key')
const state = reative({
  [key]: 'symbol value'
})
state[key]

如果值为Ref返回该值的value,看到这里如果大家有了解过ref api的话就知道了，由于ref它自己实现了自己的get,set,所以不再需要执行后面的逻辑，这个在后面会讲

调用track

递归深度观测，使整个对象都为响应式

下面我会详细讲解

track

在讲它之前，先了解它有哪些参数

 target: any, // 目标对象
 type: OperationTypes, // 追踪数据变化类型，这里是get
 key?: string | symbol // 需要获取的key
 export const enum OperationTypes {
   SET = 'set',
   ADD = 'add',
   DELETE = 'delete',
   CLEAR = 'clear',
   GET = 'get',
   HAS = 'has',
   ITERATE = 'iterate' 
 }

export function track(
 target: any,
 type: OperationTypes,
 key?: string | symbol
) {
 if (!shouldTrack) {
  return
 }
 // 获取activeReactiveEffectStack中的依赖
 const effect = activeReactiveEffectStack[activeReactiveEffectStack.length - 1]
 if (effect) {
  if (type === OperationTypes.ITERATE) {
   key = ITERATE_KEY
  }
  // 获取目标对象对应的依赖map
  let depsMap = targetMap.get(target)
  if (depsMap === void 0) {
   targetMap.set(target, (depsMap = new Map()))
  }
  // 获取对应属性的依赖
  let dep = depsMap.get(key as string | symbol)
  // 如果该依赖不存在
  if (!dep) {
   // 设置属性对应依赖
   depsMap.set(key as string | symbol, (dep = new Set()))
  }
  // 如果属性对应依赖set中不存在该依赖
  if (!dep.has(effect)) {
   // 添加到依赖set中
   dep.add(effect)
   effect.deps.push(dep)
   if (__DEV__ && effect.onTrack) {
    // 调用onTrack钩子
    effect.onTrack({
     effect,
     target,
     type,
     key
    })
   }
  }
 }
}

activeReactiveEffectStack我两次提到，从它这里拿到了依赖，注意后面执行完依赖后，会从它里面弹出

如果effect存在

从targetMap中获取对象，对饮的Map,具体的数据结构类似这样

const state = reative({
  count: 0
})
effect(() => {
 console.log(state.count) 
})
 
// 依赖大致结构(随便写的,不太规范)
{
  target(state):Map {
    count: Set (componentEffect渲染依赖, user自己添加的依赖)
  }
}

如果该对象不存在Map,就初始化一个

如果该Map中属性对应的Set不存在，就初始化一个Set

添加依赖到Set中

添加依赖到effect自身的deps数组中

最后调用onTrack回调

// 调用onTrack钩子
effect.onTrack({
  effect,
  target,
  type,
  key
})

OK,Track实现大体就这样，是不是也很简单，有了这些基础，后面要讲的一些API就很容易理解了

set

当我们点击按钮后，就会触发set属性访问器

function set(
 target: any,
 key: string | symbol,
 value: any,
 receiver: any
): boolean {
 value = toRaw(value)
 const hadKey = hasOwn(target, key)
 const oldValue = target[key]
 // 如果旧的值是ref,而新的值不是ref
 if (isRef(oldValue) && !isRef(value)) {
  // 直接更改原始ref即可
  oldValue.value = value
  return true
 }
 const result = Reflect.set(target, key, value, receiver)
 // don't trigger if target is something up in the prototype chain of original
 if (target === toRaw(receiver)) {
  /* istanbul ignore else */
  if (__DEV__) {
   const extraInfo = { oldValue, newValue: value }
   if (!hadKey) {
    trigger(target, OperationTypes.ADD, key, extraInfo)
   } else if (value !== oldValue) {
    trigger(target, OperationTypes.SET, key, extraInfo)
   }
  } else {
   if (!hadKey) {
    trigger(target, OperationTypes.ADD, key)
   } else if (value !== oldValue) {
    trigger(target, OperationTypes.SET, key)
   }
  }
 }
 return result
}

判断旧值是ref,新值不是ref

// 这种情况
const val = ref(0)
const state = reative({
  count: val
})
state.count = 1
// 其实state.count最终还是ref,还是能通过value访问
state.count.value // 1

调用Reflect.set修改值

开发环境下，拿到新旧值组成的对象，调用trigger，为什么开发环境要这么做呢，其实是为了方便onTrigger能拿到新旧值

trigger(target, OperationTypes.ADD, key, extraInfo)

可以看到第二个参数和track是一样的enum，有两种情况，一种我们设置了新的属性和值，另一种修改了原有属性值，下面我们来看看trigger实现。

trigger

export function trigger(
 target: any,
 type: OperationTypes,
 key?: string | symbol,
 extraInfo?: any
) {
 const depsMap = targetMap.get(target)
 if (depsMap === void 0) {
  // never been tracked
  return
 }
 // effect set
 const effects: Set<ReactiveEffect> = new Set()
 // computed effect set
 const computedRunners: Set<ReactiveEffect> = new Set()
 
 if (type === OperationTypes.CLEAR) {
  depsMap.forEach(dep => {
   addRunners(effects, computedRunners, dep)
  })
 } else {
  // 添加effect到set中
  if (key !== void 0) {
   addRunners(effects, computedRunners, depsMap.get(key as string | symbol))
  }
  // also run for iteration key on ADD | DELETE
  if (type === OperationTypes.ADD || type === OperationTypes.DELETE) {
   const iterationKey = Array.isArray(target) ? 'length' : ITERATE_KEY
   addRunners(effects, computedRunners, depsMap.get(iterationKey))
  }
 }
 
 // 执行set中的effect
 const run = (effect: ReactiveEffect) => {
  scheduleRun(effect, target, type, key, extraInfo)
 }
 computedRunners.forEach(run)
 effects.forEach(run)
}

看到这个函数开始的targetMap，大家应该很清楚要干嘛了吧,没错，拿到对象的Map,它包含了属性的所有依赖

如果没有Map直接返回
创建了两个Set,要干嘛用呢

 // 用来保存将要执行的依赖
 const effects: Set<ReactiveEffect> = new Set()
 // computed依赖，因为trigger不仅是要处理effect,watch,还要处理computed惰性求值的情况
 const computedRunners: Set<ReactiveEffect> = new Set()

处理三种情况CLEAR,ADD,DELETE,SET(这里没有标识)

// effect set
const effects: Set<ReactiveEffect> = new Set()
// computed effect set
const computedRunners: Set<ReactiveEffect> = new Set()
 
function addRunners(
 effects: Set<ReactiveEffect>,
 computedRunners: Set<ReactiveEffect>,
 effectsToAdd: Set<ReactiveEffect> | undefined
) {
 if (effectsToAdd !== void 0) {
  effectsToAdd.forEach(effect => {
   if (effect.computed) {
    computedRunners.add(effect)
   } else {
    effects.add(effect)
   }
  })
 }
}

可以看到，三种情况实际上都差不多，唯一的区别就是，如果添加的对象是数组,就会拿到length属性的依赖，用于修改数组长度

if (type === OperationTypes.ADD || type === OperationTypes.DELETE) {
  const iterationKey = Array.isArray(target) ? 'length' : ITERATE_KEY
  addRunners(effects, computedRunners, depsMap.get(iterationKey))
}

执行属性对应的依赖

 // 执行set中的effect
 const run = (effect: ReactiveEffect) => {
  scheduleRun(effect, target, type, key, extraInfo)
 }
 
 computedRunners.forEach(run)
 effects.forEach(run)

function scheduleRun(
 effect: ReactiveEffect,
 target: any,
 type: OperationTypes,
 key: string | symbol | undefined,
 extraInfo: any
) {
 if (__DEV__ && effect.onTrigger) {
  effect.onTrigger(
   extend(
    {
     effect,
     target,
     key,
     type
    },
    extraInfo // { oldValue, newValue: value }
   )
  )
 }
 if (effect.scheduler !== void 0) {
  effect.scheduler(effect)
 } else {
  effect()
 }
}

最后调用了scheduleRun,它内部会分别执行onTrigger,scheduler，effect

需要注意的是，只有开发环境才会执行onTrigger,这也是为什么，前面要这么判断

if (__DEV__) {
  const extraInfo = { oldValue, newValue: value }
  if (!hadKey) {
    trigger(target, OperationTypes.ADD, key, extraInfo)
  } else if (value !== oldValue) {
    trigger(target, OperationTypes.SET, key, extraInfo)
  }
}

readonly

有了前面的基础，readonly看起来会非常简单，唯一的区别就是rawToReadonly,rawToReadonly, readonlyHandlers

export function readonly(target: object) {
 
 if (reactiveToRaw.has(target)) {
  target = reactiveToRaw.get(target)
 }
 return createReactiveObject(
  target,
  rawToReadonly,
  readonlyToRaw,
  readonlyHandlers,
  readonlyCollectionHandlers
 )
}

前两个大家应该能猜出来了，关键是最后这个readonlyHandlers,区别就在set

 set(target: any, key: string | symbol, value: any, receiver: any): boolean {
  if (LOCKED) {
   if (__DEV__) {
    console.warn(
     `Set operation on key "${key as any}" failed: target is readonly.`,
     target
    )
   }
   return true
  } else {
   return set(target, key, value, receiver)
  }
 }

它的实现很简单，不过LOCKED有是什么鬼，大家可以找到lock.ts

//vue-next\packages\reactivity\src\lock.ts
export let LOCKED = true
 
export function lock() {
 LOCKED = true
}
 
export function unlock() {
 LOCKED = false
}

看似简单，但是却非常重要，它能够控制被readonly的对象能够暂时被更改，就比如我们常用的props,它是无法被修改的,但是Vue内部又要对他进行更新，那怎么办，话不多说，我们再源码中看他具体应用

// vue-next\packages\runtime-core\src\componentProps.ts
export function resolveProps(
 instance: ComponentInternalInstance,
 rawProps: any,
 _options: ComponentPropsOptions | void
) {
 const hasDeclaredProps = _options != null
 const options = normalizePropsOptions(_options) as NormalizedPropsOptions
 if (!rawProps && !hasDeclaredProps) {
  return
 }
 const props: any = {}
 let attrs: any = void 0
 
 const propsProxy = instance.propsProxy
 const setProp = propsProxy
  ? (key: string, val: any) => {
    props[key] = val
    propsProxy[key] = val
   }
  : (key: string, val: any) => {
    props[key] = val
   }
 
 unlock()
 
 // 省略一些修改props操作。。
  
 lock()
 
 instance.props = __DEV__ ? readonly(props) : props
 instance.attrs = options
  ? __DEV__ && attrs != null
   ? readonly(attrs)
   : attrs
  : instance.props
}

这里前后分别调用了unlock和lock,这样就可以控制对readonly属性的修改

那么readonly的讲解就到这了

computed

export function computed<T>(
 getterOrOptions: (() => T) | WritableComputedOptions<T>
): any {
 const isReadonly = isFunction(getterOrOptions)
 const getter = isReadonly
  ? (getterOrOptions as (() => T))
  : (getterOrOptions as WritableComputedOptions<T>).get
 const setter = isReadonly
  ? null
  : (getterOrOptions as WritableComputedOptions<T>).set
 
 let dirty: boolean = true
 let value: any = undefined
 
 const runner = effect(getter, {
  lazy: true,
  computed: true,
  scheduler: () => {
   dirty = true
  }
 })
 return {
  _isRef: true,
  // expose effect so computed can be stopped
  effect: runner,
  get value() {
   if (dirty) {
    value = runner()
    dirty = false
   }
   trackChildRun(runner)
   return value
  },
  set value(newValue) {
   if (setter) {
    setter(newValue)
   } else {
    // TODO warn attempting to mutate readonly computed value
   }
  }
 }
}

首先是前面这段

 const isReadonly = isFunction(getterOrOptions)
 const getter = isReadonly
  ? (getterOrOptions as (() => T))
  : (getterOrOptions as WritableComputedOptions<T>).get
 const setter = isReadonly
  ? null
  : (getterOrOptions as WritableComputedOptions<T>).set

大家都知道computed是可以单独写一个函数，或者get,set访问的，这里不多讲

然后调用了effect,这里lazy设置为true, scheduler可以更改dirty为true

const runner = effect(getter, {
  lazy: true,
  computed: true,
  scheduler: () => {
    dirty = true
  }
})

然后我们具体来看看，返回的对象

{
  _isRef: true,
  // expose effect so computed can be stopped
  effect: runner,
  get value() {
   if (dirty) {
    value = runner()
    dirty = false
   }
   trackChildRun(runner)
   return value
  },
  set value(newValue) {
   if (setter) {
    setter(newValue)
   } else {
    // TODO warn attempting to mutate readonly computed value
   }
  }
 }

先说说set吧，尤大似乎还没写完，只是单纯能修改值

然后是get,注意dirty的变化，如果computed依赖了state中的值，初次渲染时，他会调用依赖，然后dirty = false，关键来了，最后执行了trackChildRun

function trackChildRun(childRunner: ReactiveEffect) {
 const parentRunner =
  activeReactiveEffectStack[activeReactiveEffectStack.length - 1]
 if (parentRunner) {
  for (let i = 0; i < childRunner.deps.length; i++) {
   const dep = childRunner.deps[i]
   if (!dep.has(parentRunner)) {
    dep.add(parentRunner)
    parentRunner.deps.push(dep)
   }
  }
 }
}

由于computed是依赖了state中的属性的，一旦在初始时触发了get,执行runner，就会将依赖收集到activeReactiveEffectStack中，最后才是自己的依赖，栈的顶部是state属性的依赖

if (!dep.has(parentRunner)) {
  dep.add(parentRunner)
  parentRunner.deps.push(dep)
}

所以最后这段代码实现了state属性变化后，才导致了computed依赖的调用，从而惰性求值

ref

const convert = (val: any): any => (isObject(val) ? reactive(val) : val)
export function ref<T>(raw: T): Ref<T> {
 raw = convert(raw)
 const v = {
  _isRef: true,
  get value() {
   track(v, OperationTypes.GET, '')
   return raw
  },
  set value(newVal) {
   raw = convert(newVal)
   trigger(v, OperationTypes.SET, '')
  }
 }
 return v as Ref<T>
}