Vue3 响应式原理

响应式原理

Vue2 使用的是 Object.defineProperty Vue3 使用的是 Proxy

2.0的不足

对象只能劫持设置好的数据，新增的数据需要Vue.Set(xxx) 数组只能操作七种方法，修改某一项值无法劫持。

reactive和effect的实现

export const reactive = <T extends object>(target:T) => {
    return new Proxy(target,{
        get (target,key,receiver) {
          const res  = Reflect.get(target,key,receiver) as object


          return res
        },
        set (target,key,value,receiver) {
           const res = Reflect.set(target,key,value,receiver)


           return res
        }
    })
}

Vue3 的响应式原理依赖了 Proxy 这个核心 API，通过 Proxy 可以劫持对象的某些操作。

effect track trigger

实现effect 副作用函数

let activeEffect;
export const effect = (fn:Function) => {
     const _effect = function () {
        activeEffect = _effect;
        fn()
     }
     _effect()
}

使用一个全局变量 active 收集当前副作用函数，并且初始化的时候调用一下

实现track

const targetMap = new WeakMap()
export const track = (target,key) =>{
   let depsMap = targetMap.get(target)
   if(!depsMap){
       depsMap = new Map()
       targetMap.set(target,depsMap)
   }
   let deps = depsMap.get(key)
   if(!deps){
      deps = new Set()
      depsMap.set(key,deps)
   }

   deps.add(activeEffect)
}

执行完成成后我们得到一个如下的数据结构

实现trigger

export const trigger = (target,key) => {
   const depsMap = targetMap.get(target)
   const deps = depsMap.get(key)
   deps.forEach(effect=>effect())
}

当我们进行赋值的时候会调用 set 然后触发收集的副作用函数

import {track,trigger} from './effect'


export const reactive = <T extends object>(target:T) => {
    return new Proxy(target,{
        get (target,key,receiver) {
          const res  = Reflect.get(target,key,receiver) as object

          track(target,key)

          return res
        },
        set (target,key,value,receiver) {
           const res = Reflect.set(target,key,value,receiver)
 
           trigger(target,key)

           return res
        }
    })
}

给 reactive 添加这两个方法

测试代码

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <div id="app">

    </div>

    <script type="module">
        import { reactive } from './reactive.js'
        import { effect } from './effect.js'
        const user = reactive({
            name: "小满",
            age: 18
        })
        effect(() => {
            document.querySelector('#app').innerText = `${user.name} - ${user.age}`
        })

        setTimeout(()=>{
            user.name = '大满很吊'
            setTimeout(()=>{
                user.age = '23'
            },1000)
        },2000)

    </script>
</body>

</html>

递归实现reactive

import { track, trigger } from './effect'

const isObject = (target) => target != null && typeof target == 'object'

export const reactive = <T extends object>(target: T) => {
    return new Proxy(target, {
        get(target, key, receiver) {
            const res = Reflect.get(target, key, receiver) as object

            track(target, key)

            if (isObject(res)) {
                return reactive(res)
            }

            return res
        },
        set(target, key, value, receiver) {
            const res = Reflect.set(target, key, value, receiver)

            trigger(target, key)

            return res
        }
    })
}

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <div id="app">

    </div>

    <script type="module">
        import { reactive } from './reactive.js'
        import { effect } from './effect.js'
        const user = reactive({
            name: "小满",
            age: 18,
            foo:{
                bar:{
                    sss:123
                }
            }
        })
        effect(() => {
            document.querySelector('#app').innerText = `${user.name} - ${user.age}-${user.foo.bar.sss}`
        })

        setTimeout(()=>{
            user.name = '大满很吊'
            setTimeout(()=>{
                user.age = '23'
                setTimeout(()=>{
                    user.foo.bar.sss = 66666666
                },1000)
            },1000)
        },2000)

    </script>
</body>

</html>