手写promise

function MyPromise(executor){
        this.status = 'pending' // 状态  pengding success fail
        this.result = '' //结果
        this.onSuccessArr = [] //成功回调数组
        this.onFailArr = [] //失败回调数组
        resolve =(val)=>{ //返回成功
            if(this.status!=='pending') return  // 以第一次执行为准 后续状态不允许更改
            this.result = val
            this.status = 'success'
            while (this.onSuccessArr.length) {
                 //将保存的多个then头部删除并执行直到数组为空
                this.onSuccessArr.shift()(this.result)
            }
        }
        reject = (val) =>{ // 返回失败
            if(this.status!=='pending') return  // 以第一次执行为准 后续状态不允许更改
            this.result = val
            this.status = 'fail'
            while (this.onFailArr.length) {
                //将保存的多个then头部删除并执行直到数组为空
                this.onFailArr.shift()(this.result)
            }
        }
        try{ //如果异常就执行reject
            executor(resolve,reject) 
        }catch(e){
            reject(e)
        }

    }

    MyPromise.prototype.then = function (onSuccess,onFail){
        //接受成功和失败两个函数
        onSuccess = typeof onSuccess === 'function' ? onSuccess : val => val
        onFail = typeof onFail === 'function' ? onFail : reason => { throw reason }
        //链式调用 返回一个新的promise对象
        const newPromise = new MyPromise((resolve,reject)=>{
            const resolvePromise = cb => {
                try {
                    // 执行回调的onSuccess函数
                    const x = cb(this.result)
                    //判断返回的是否是promise对象
                    if (x instanceof MyPromise) {
                        x.then(resolve, reject)
                    } else {
                        // 非Promise就直接成功
                        resolve(x)
                    }
                } catch (err) {
                    // 处理报错
                    reject(err)
                    throw new Error(err)
                }
            }

            if (this.status === 'success') {
                // 如果当前为成功状态，执行第一个回调
                resolvePromise(onSuccess)
            } else if (this.status === 'fail') {
                // 如果当前为失败状态，执行第二哥回调
                resolvePromise(onFail)
            }else if (this.status === 'pending'){ 
                //如果是pending状态 定时器还没执行 就讲他们抛进数组
                this.onSuccessArr.push(onSuccess.bind(this))
                this.onFailArr.push(onFail.bind(this))
            }
        })
        return newPromise
    }   

    const promise1 = new MyPromise((resolve,reject)=>{
        // setTimeout(()=>{
        //     resolve(1)
        // })
        resolve(1)
    })
    promise1.then((res)=>{
        return new MyPromise((resolve)=>resolve(333))
    }).then((res)=>{
        console.log(res)
    })