Vue3响应式原理-computed

接受一个 getter 函数，并根据 getter 的返回值返回一个不可变的响应式 ref 对象。

import { isFunction } from "@vue/shared";
import { activeEffect, ReactiveEffect, trackEffects, triggerEffects } from "./effect";

class ComputedRefImpl {
    public effect;
    public _value;
    public dep;
    public _dirty = true;
    constructor(getter,public setter) {
        this.effect = new ReactiveEffect(getter,()=>{ 
            if(!this._dirty){ // 依赖的值变化更新dirty并触发更新
                this._dirty = true;
                triggerEffects(this.dep)
            }
        });
    }
    get value(){ // 取值的时候进行依赖收集
        if(activeEffect){
            trackEffects(this.dep || (this.dep = new Set));
        }
        if(this._dirty){ // 如果是脏值, 执行函数
            this._dirty = false;
            this._value = this.effect.run(); 
        }
        return this._value; 
    }
    set value(newValue){
        this.setter(newValue)
    }
}
export function computed(getterOrOptions) {
    const onlyGetter = isFunction(getterOrOptions); // 传入的是函数就是getter
    let getter;
    let setter;
    if (onlyGetter) {
        getter = getterOrOptions;
        setter = () => { }
    } else {
        getter = getterOrOptions.get;
        setter = getterOrOptions.set;
    }
    // 创建计算属性
    return new ComputedRefImpl(getter, setter)

创建ReactiveEffect时，传入scheduler函数，稍后依赖的属性变化时调用此方法！

export function triggerEffects(effects) { 
    effects = new Set(effects);
    for (const effect of effects) {
        if (effect !== activeEffect) { // 如果effect不是当前正在运行的effect
            if (effect.scheduler) {
                effect.scheduler()
            } else {
                effect.run(); // 重新执行一遍
            }
        }
    }
}
export function trackEffects(dep) { // 收集dep 对应的effect
    let shouldTrack = !dep.has(activeEffect)
    if (shouldTrack) {
        dep.add(activeEffect);
        activeEffect.deps.push(dep); 
    }
}