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}
}