手写Promise.all

Promise._all = function (promises) {
  // 该方法返回一个promise对象
  return new Promise((resolve, reject) => {
    // 该方法的参数需为一个可迭代对象
    if (promises == null || typeof promises[Symbol.iterator] !== "function") {
      throw new TypeError(`${promises} is not a iterable`);
    }
    promises = [...promises];

    // 可迭代对象为空则返回已resolve的promise
    if (promises.length === 0) {
      resolve([]);
    }

    let count = 0;
    const values = [];
    promises.forEach((promise, index) => {
      // 保证可迭代对象的元素为promise，使用Promise.resolve()处理
      Promise.resolve(promise)
        .then((res) => {
          values[index] = res;
          if (++count === promises.length) resolve(values);
        })
        .catch(reject);
    });
  });
};

Promise.myAll = function (proms) {
    let res, rej
    const p = new Promise((resolve, reject) => {
        res = resolve()
        rej = reject()

    })
    let i = 0
    let fulfilled = 0
    const result = []

    for (const prom of proms) {
        const index = i
        i++
        Promise.resolve(prom).then((data) => {
            // 完成的数据汇总到最终结果
            result[index] = data;
            //判断是否全部完成
            fulfilled++
            if (fulfilled === i) {
                res(result)
            }
        }, rej)
    }
    if (i === 0) {
        res([])
    }

    return p
}

Promise.myAll([]).then((res) => {
    console.log(res);
})

github地址：s

https://github.com/lydiahallie/javascript-questions/blob/master/zh-CN/README-zh_CN.md