Promise简单实现

class MyPro {
    constructor(func) {
        this.state = "pending"; // or full or rejected
        this.value = undefined;
        this.tasks = [];
        this.errortasks = [];
        this.finnalytasks = [];
        function resolve(value) {
            if (this.state === "pending") {
                this.value = value;
                this.state = "full";
                this._gg(this.value);
                this
                    .tasks
                    .forEach(func => {
                        setTimeout(() => {
                            this.value = func(this.value)
                        })
                    });
            } else {
                return
            }

        }
        function reject(reason) {
            if (this.state === "pending") {
                this.state = "rejected";
                this
                    .errortasks
                    .forEach(func => {

                        setTimeout(() => {
                            if (typeof func === "function") {
                                func(reason)
                            }

                        })
                    });
            } else {
                return
            }
        }
        try {
            setTimeout(()=>func(resolve.bind(this), reject.bind(this)))
        } catch (e) {
            reject(e);
        } finally {
            setTimeout(() => {
                this
                    .finnalytasks
                    .forEach(func => setTimeout(() => {
                        func()
                    }))
            })

        }
    };
    then(onFulfilled, onRejected) {
        if (this.state === "pending") {
            this
                .tasks
                .push(onFulfilled)
            this
                .errortasks
                .push(onRejected)
        }
        return this;
    }; 
    catch (rejectFunc) {
        if (this.state === "pending") {
            this
                .errortasks
                .push(rejectFunc)
        }
        return this;
    };
    _gg(v){
        //提供个观察者模式接口

    }
    static resolve(val){
        return new MyPro((rel) =>rel(val))
    }
    static reject(){}
    static race(arr){
        return new MyPro((rel) =>{
            //当某一个触发就触发

            arr.forEach(item => {
                item._gg = (v) => rel(v)
            });

        })
    }
    static all(arr){
        let ps = arr.length;
        const result = [];
        return new MyPro((rel) =>{
            arr.forEach(item => {
                item._gg = (v) => {

                }
            })
            rel(result);
        })
    }
}