一.reactive与effect功能

reactive方法会将对象变成proxy对象， effect中使用reactive对象时会进行依赖收集，稍后属性变化时会重新执行effect函数。

<div id="app"></div><script type="module">import {reactive,effect,} from "/node_modules/@vue/reactivity/dist/reactivity.esm-browser.js";//   reactive创建一个响应式对象//   effect 副作用函数，默认执行一次，数据变化后再次执行const state = reactive({ name: "orange", age: 18 });effect(() => {document.getElementById("app").innerHTML = state.name;});console.log(state);setTimeout(() => {state.name = "apple";}, 2000);</script>

二.reactive与effect实现

1.实现reactive

1.1 get、set基础实现

// reactive.ts
import { isObject } from "@vue/shared";const mutableHandlers = {get(target, key, receiver) {return Reflect.get(target, key, receiver);},set(target, key, value, receiver) {return Reflect.set(target, key, value, receiver);},
};export function reactive(target) {if (!isObject(target)) {return target;}const proxy = new Proxy(target, mutableHandlers);return proxy;
}

如下图，如果采用target[key]方法，获取aliasName时 不会触发name的get

1.2 完善重复

const state = { name: "orange", age: 18 };const p1 = reactive(state);const p2 = reactive(state);const p3 = reactive(p1);console.log(p1 === p2);console.log(p1 === p3);

• 响应式数据缓存，防止重复代理
  使用map，key为对象，值为响应式对象，实现p1 === p2

const reactiveMap = new WeakMap(); //内存泄漏
export function reactive(target) {if (!isObject(target)) {return target;}const exitProxy = reactiveMap.get(target);if (exitProxy) {return exitProxy;}const proxy = new Proxy(target, mutableHandlers);reactiveMap.set(target, proxy);return proxy;
}

• 响应式数据标记
  用枚举做标记，响应式对象都有get和set方法，p1初次创建时state没有get和set方法，target[ReactiveFlags.IS_REACTIVE]取值为false，创建p3时，p1响应式，取值为true,直接返回p1

export const enum ReactiveFlags {IS_REACTIVE = "__v_isReactive",
}get(target, key, receiver) {if (ReactiveFlags.IS_REACTIVE == key) {return true;}return Reflect.get(target, key, receiver);},export function reactive(target) {...,if (target[ReactiveFlags.IS_REACTIVE]) {return target;}const proxy = new Proxy(target, mutableHandlers);reactiveMap.set(target, proxy);return proxy;
}

2.实现effect

2.1 effect函数

vue2与vue3早期的依赖收集采用的都是栈方式存储，vue3后来改为树型数据存储。
effect执行时，把当前effect作为全局的，触发属性的get方法，收集依赖

let activeEffect;
class ReactiveEffect {public deps: Array<any> = []; // 判断依赖属性public active: boolean = true; // 是否激活public parent = undefined; constructor(public fn) {}run() {if (!this.active) {return this.fn();}try {this.parent = activeEffect;activeEffect = this;return this.fn();} finally {activeEffect = this.parent;this.parent = undefined;}}
}
export function effect(fn) {const _effect = new ReactiveEffect(fn);_effect.run();
}

2.2 依赖收集

执行effect时，会触发依赖属性的get方法，在属性的get中进行依赖收集

get(target, key, receiver) {if (ReactiveFlags.IS_REACTIVE == key) {return true;}console.log(activeEffect, key);track(target,key)return Reflect.get(target, key, receiver);},

/* 属性变动后 要重新执行run 需要把属性和effect关联起来 收集对象上属性关联的effect不能光记录属性，容易两个对象有重名的属性，所以需要带着对象记录target为对象let mapping = {target:{name:[effect1,effect2,effect3] 一个属性可以在多个页面使用}}*/
const targetMap = new WeakMap();
export function track(target, key) {// 如果取值操作没有发生在effect中，则不需要收集依赖if (!activeEffect) {return;}// 判断是否已经记录过let depsMap = targetMap.get(target);if (!depsMap) {targetMap.set(target, (depsMap = new Map()));}let dep = depsMap.get(key);if (!dep) {// 值为一个不重复数组depsMap.set(key, (dep = new Set()));}let shouldTrack = !dep.has(key);if (shouldTrack) {dep.add(activeEffect);activeEffect.deps.push(dep); //同时effect记住当前这个属性}
}

2.3 属性更改 触发effect

 set(target, key, value, receiver) {// 数据变化后触发对应的effect方法const oldValue = target[key];let r = Reflect.set(target, key, value, receiver);if (oldValue != value) {trigger(target, key, value, oldValue);}return r;},

export function trigger(target, key, newValue, oldValue) {// 通过对象找到对应的属性 让这个属性对应的effect重新执行const depsMap = targetMap.get(target);if (!depsMap) {return;}const dep = depsMap.get(key); // name 或者 age对应的所有effectconst effects = [...dep];// 运行的是数组 删除的是seteffects &&effects.forEach((effect) => {// 正在执行的effect ，不要多次执行if (effect !== activeEffect) effect.run();});}

2.4 清除effect依赖

const state = reactive({ flag: true, name: "orange", age: 18 });effect(() => {// 副作用函数 (effect执行渲染了页面)console.log("render");document.body.innerHTML = state.flag ? state.name : state.age;});setTimeout(() => {state.flag = false;setTimeout(() => {console.log("修改name，原则上不更新");state.name = "zf";}, 1000);}, 1000);

当切换flag时，effect的依赖已经更新，但是修改name又触发了依赖，需要在每次收集依赖前先清空

function cleanupEffect(effect) {let { deps } = effect; // 清理effectfor (let i = 0; i < deps.length; i++) {deps[i].delete(effect);}effect.deps.length = 0;
}

为了避免无限循环页面卡死情况，触发依赖时拷贝出来一份属性对应的effect列表，因为清除的时候在删除effect，边删除边添加会造成死循环

2.5 effect失活

通过effect返回当前effect实例，然后curEffect.effect.stop()调用stop方法

let runner = effect(() => {// 副作用函数 (effect执行渲染了页面)console.log("render");document.body.innerHTML = state.flag ? state.name : state.age;});runner.effect.stop()

  stop() {cleanupEffect(this);this.active = false;}export function effect(fn) {const _effect = new ReactiveEffect(fn);_effect.run();const runner = _effect.run.bind(_effect); //调用effect.effect.stop() 停止effectrunner.effect = _effect;return runner;
}

失活后我们可以手动调用 runner()触发effect方法

2.6 调度执行

trigger触发时，我们可以自己决定副作用函数执行的时机、次数、及执行方式

export function effect(fn, options:any = {}) {const _effect = new ReactiveEffect(fn,options.scheduler); // 创建响应式effect// if(options){//     Object.assign(_effect,options); // 扩展属性// }_effect.run(); // 让响应式effect默认执行const runner = _effect.run.bind(_effect);runner.effect = _effect;return runner; // 返回runner
}export function trigger(target, type, key?, newValue?, oldValue?) {const depsMap = targetMap.get(target);if (!depsMap) {return}let effects = depsMap.get(key);if (effects) {effects = new Set(effects);for (const effect of effects) {if (effect !== activeEffect) { if(effect.scheduler){ // 如果有调度函数则执行调度函数effect.scheduler()}else{effect.run(); }}}}
}