Promise.myAll = function(list) {

    const results = []

    let count = 0

    return new Promise((resolve, reject) => {

        list.map((item, index) => {

            // 把数据都处理成Promise

            Promise.resolve(item).then(

                res => {

                    results[index] = res

                    count += 1

                    if (count == list.length) {

                        resolve(results)

                    }

                },

                err => {

                    reject(err)

                }

            )

        })

    })

}

​

const promise1 = Promise.resolve(3);

const promise2 = 42;

const promise3 = new Promise((resolve, reject) => {

  setTimeout(resolve, 100, 'foo');

});

​

const promise4 = new Promise((resolve, reject) => {

  setTimeout(reject, 100, 'foo');

});

​

Promise.all([promise1, promise2, promise3]).then((values) => {

  console.log(values, 'Promise.all');

});

​

Promise.myAll([promise1, promise2, promise3]).then((values) => {

  console.log(values, 'Promise.myAll');

});

​

Promise.myAll([promise1, promise2, promise3, promise4]).then((values) => {

  console.log(values, 'Promise.myAll');

}, err => {

  console.log(err, 'Promise.myAll失败');

});