手写promise（1）

class Promise{

    constructor(excutorCallBack){

        this.status = 'pending'

        this.value = undefined;

        this.fulfilledAry = []; //管控，必须得then执行后才能执行resolveFn方法，成功要做的方法

        this.rejectedAry = []; //失败要做的方法

        // => 执行EXCUTOP

        let resolveFn = (result) =>{

            let timer = setTimeout(()=>{

                if(this.status !== 'pending') return;

                    clearTimeout(timer)

                    this.status = 'fulfilled';

                    this.value = result;

                    this.fulfilledAry.forEach(item=>item(this.value))

            },0)

        };

        let rejectFn = (reason) =>{

            let timer = setTimeout(()=>{

                clearTimeout(timer)

                if(this.status !== 'pending') return;

                this.status = 'rejected';

                this.value = reason;

                this.rejectedAry.forEach((item)=>item(this.value))

            },0)

        }

        // => 执行EXCUTOP（异常捕获）

        try{

            excutorCallBack(resolveFn,rejectFn);

        } catch (err){

            // 有异常信息按照rejected状态信息处理

            rejectFn(err);

        }

    }

    then (fulfilledCallBack,rejectedCallBack) {

        this.fulfilledAry.push(fulfilledCallBack);

        this.rejectedAry.push(rejectedCallBack);

    }

}

module.exports = Promise;