promise简易版

class Promises {
constructor(cb) {
this.thenArr = []; //存放then函数里面的成功的函数和失败的函数
this.cb = cb; //promise中的回调函数
this.count = 0; //计数
this.returnText = null;//返回值
this.resolve = this.resolve.bind(this);
this.reject = this.reject.bind(this);
this.cb(this.resolve, this.reject);
}

    static all(promiseData) {
        let resultData = [];
        let errData = [];
        return new Promises((res, rej) => {
            promiseData.forEach(i => {
                i.then(data => {
                    resultData.push(data);
                    test();
                }, (err) => {
                    errData.push(err);
                    testerr();
                })
            })

            function test() {
                if (promiseData.length === resultData.length) {
                    res(resultData)
                }
            }
 
            function testerr() {
                if (errData.length > 0) {
                    rej(errData[0])
                }
            }
        })
    }

    static race(promiseData) {
        let resultData = [];
        let errData = [];
        return new Promises((res, rej) => {
            promiseData.forEach(i => {
                i.then(data => {
                    resultData.push(data);
                    test();
                }, (err) => {
                    errData.push(err);
                    testerr();
                })
            })

            function test() {
                if (promiseData.length > resultData.length) {
                    res(resultData)
                }
            }

            function testerr() {
                if (errData.length === errData.length) {
                    rej(errData[0])
                }
            }
        })
    }
    resolve(data) {
        // 判断返回值的状态
        // 1.返回值是promise
        //2.返回值是普通的
        let rest = this.thenArr.slice(this.count)
        if (this.returnText && this.returnText instanceof Promises) {
            rest.forEach(item => {
                this.returnText.then(item.okCb, item.errCn);
            })
            return;
        } else if(this.returnText) {
            this.thenArr[this.count].okCb(this.returnText);
        } else {
            this.returnText = this.thenArr[this.count].okCb(data);
        }
        this.count++;
        if (this.count < this.thenArr.length) {
            this.resolve(data);
        }
    }
    reject(err){
        //如果失败，根据count执行当前then函数的失败函数
        this.thenArr[this.count].errCn(err)
        //如果失败的then函数下面还有未执行的then函数，则直接调用下一个then函数的成功函数
        this.count++
        if(this.count<this.thenArr.length){
            this.resolve()
        }
    }
    then(okCb, errCn) {
        this.thenArr.push({
            okCb,
            errCn
        })
        return this;
    }   
}



let pro1=()=>{
    return new Promises((resolve,reject)=>{
        setTimeout(()=>{
            reject(1)
        },1000)
    })
}

let pro2=()=>{
    return new Promises((resolve,reject)=>{
        setTimeout(()=>{
            reject(2)
        },2000)
    })
}

Promises.race([pro1(),pro2()]).then((data)=>{
    console.log(data)
},(err)=>{
    console.log(err+"2344")
})


// new Promises((res, rej) => {
//     setTimeout(() => {
//     rej(123)
//     }, 1000)
// }).then((data) => {
//     console.log(data)
// }, (err) => {
//     console.log('err', err)
// }).then((data) => {
//     return new Promise((res, rej) => {
//         res(456)
//     })
// }).then((data) => {
//     console.log(data)
// })