Vue3响应式

• track() 保存代码
• effect() 需要运行代码
• trigger() 运行所有存储的代码

let dep = new Set(); 
let effect = ()=>{total=price * quantity}
function track(){dep.add(effect)}
function trigger(){dep.forEach(effect=>effect())}

引入depsMap（一个depsMap对应一个响应式对象），一个dep对应一个响应式对象上的属性

const depsMap = new Map();
function track(key){
    let dep = depsMap.get(key);
    if(!dep){
        depsMap.set(key,(dep = new Set()));
    }
    dep.add(effect);
}
function trigger(key){
    let dep = depsMap.get(key);
    if(dep){
        dep.forEach(effect=>effect())
    }
}

targetMap（weekMap，key是object。存储所有响应式对象）

const targetMap = new WeakMap();
function track(target,key){
    let depsMap = targetMap.get(target);
    if(!depsMap){
        targetMap.set(target,(depsMap = new Map()));
    }
    let dep = depsMap.get(key);
    if(!dep){
        depsMap.set(key,(dep = new Set()));
    }
    dep.add(effect);
}
function trigger(target,key){
    let depsMap = targetMap.get(target);
    if(!depsMap){return}
    let dep = depsMap.get(key);
    if(dep){
        dep.forEach(effect=>effect())
    }
}

test

let product = {price:5,quantity:2}
let total = 0;
let effect = ()=>{
    total = product.price*product.quantity;
}
track(product,'quantity');
effect();
/*
> total //10
> trigger(product,'quantity')
> total //15
*/

question:如何自动执行？

响应式引擎

当我们运行effect，如果访问（get）了产品的属性，我们想track去保存effect，当我们（set）去改变产品的属性时，我们想用trigger去运行保存的effect

怎样去拦截GET，SET？（Proxy、reactive）

• vue2 使用了ES5 的Object.defineProperty()
• vue3 使用ES6 的Reflect 和Proxy

console.log(Reflect.get(Product,'quantity'))

function reactive(target){
    const handler = {
        get(target,key,receiver){
            let res = Reflect.get(target,key,receiver)//receiver能保证this指向正确
            track(target,key);
            return res;
        },
        set(target,key,value,receiver){
            let oldValue = target[key];
            let res = Reflect.set(target,key,value,receiver);
            if(oldValue!=res){
                trigger(target,key);
            }
             return res
        }
    }
    return new Proxy(target,handler)
}

let product = reactive({price:5,quantity:2})
let total = 0;
let effect = ()=>{
    total = product.price*product.quantity;
}
effect();
console.log(total);
product.quantity = 3;
console.log(total)

是否需要在所有地方的get上调用track？

activeEffect（优化）

仅在effect中读取时才记录

let activeEffect = null
function effect(eff){
    activeEffect = eff
    activeEffect()
    activeEffect = null
}
//..
effect(()=>{
    total = product.price*product.quantity
})

function track(target,key){
   if(activeEffect){
        let depsMap = targetMap.get(target);
        if(!depsMap){
            targetMap.set(target,(depsMap = new Map()));
        }
        let dep = depsMap.get(key);
        if(!dep){
            depsMap.set(key,(dep = new Set()));
        }
        dep.add(activeEffect);
   }
}

let product = reactive({price:5,quantity:2})
let salePrice = 0;
let total = 0;
effect(()=>{
    total = product.price*product.quantity
})
effect(()=>{
    salePrice = product.price * 0.9
})
console.log(`before update total = ${total} salePrice = ${salePrice}`)
product.quantity = 3;
console.log(`after update total = ${total} salePrice = ${salePrice}`)
product.price = 10
console.log(`after update total = ${total} salePrice = ${salePrice}`)

把product.price换成salePrice怎么实现响应式呢？

Ref

salePrice = ref(0)
effect(()=>{
    total = salePrice.value*product.quantity
})
effect(()=>{
    salePrice.value = product.price * 0.9
})

利用reactive

function ref(intiaValue){
    return reactive({value:intiaValue})
}

利用js计算属性

function ref(raw){
    const r = {
        get value(){
            track(r,'value')
            return raw
        }
        set value(newVal){
            raw = newVal; 
            trigger(r,'value')
        }
    }
    return r;
}

computed

function computed(getter){
    let res = ref();
    effect(()=>{
        res.value = getter();
    })
    return res;
}