手写Promise.all()方法

Promise.prototype.all = function (iterators) {
    const promises = Array.from(iterators)
    const promiseList = [],
        len = promises.length
    let count = 0
    return new Promise((resolve, reject) => {
        promises.forEach((promise, index) => {
            Promise.resolve(promise).then(res => {
                count++
                promiseList[index] = res
                if (count === len) {
                    resolve(promiseList)
                }
            }).catch(e => {
                reject(e)
            })
        })
    })
}

const promise1 = Promise.resolve('promise1');
const promise2 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 2000, 'promise2');
});
const promise3 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 1000, 'promise3');
});

Promise.all([promise1, promise2, promise3]).then(function(values) {
    console.log(values);
});