js 手写Promise.race

1. 入参必须实现iterator接口，一般为一个非空数组
2. 返回一个promise, 结果为数组中第一个改变为成功/失败状态的那个promise元素

    Promise._race = function (promises) {
        if (!promises instanceof Array || !promises.length) throw 'promises must be an not empty Array'
        const length = promises.length
        return new Promise((resolve, reject) => {
            for (let i = 0; i < promises.length; i++) {
                promises[i].then(v => resolve(v), r => reject(r))
            }
        })
    }

    const doAsyncTask = (fn, timeout) => setTimeout(() => fn(), timeout)
    const p1 = new Promise((resolve, reject) => doAsyncTask(()=>{resolve(1)},2000))
    const p2 = new Promise((resolve, reject) => doAsyncTask(()=>{resolve(2)},1000))
    const p3 = new Promise((resolve, reject) => doAsyncTask(()=>{resolve(3)},3000))
    const res = Promise._race([p1,p2,p3])
    res.then(v=>console.log(v),r=>console.log(r))
    console.log(res);