SOURCE

function promiseAll(iterable) {
  const isIterable = subject =>
    subject != null && typeof subject[Symbol.iterator] === 'function';
  const validateIterable = subject => {
    if (isIterable(subject)) return;

    throw new TypeError(
      `Cannot read property 'Symbol(Symbol.iterator)' of ${Object.prototype.toString.call(
        subject
      )}`
    );
  };

  const isEmptyIterable = subject => {
    for (let _ of subject) {
      return false;
    }

    return true;
  };

  return new Promise((resolve, reject) => {
    // 对输入进行检验
    validateIterable(iterable);

    let iterableSize = 0;
    const values = [];

    // 处理空输入 []
    if (isEmptyIterable(iterable)) return resolve(values);

    const add = (value, index) => {
      values[index] = value;
      if (values.filter(() => true).length === iterableSize) {
        resolve(values);
      }
    };

    for (let item of iterable) {
      ((entry, index) => {
        Promise.resolve(entry).then(value => add(value, index), reject);
      })(item, iterableSize++);
    }
  });
}

const P1 = () => {
  return new Promise((resolve, reject) => {
    console.log('-----P1 进来了呢');
    setTimeout(() => {
      console.log('P1--------');
      resolve('P111111');
    }, 500);
  });
};

const P2 = () => {
  return new Promise((resolve, reject) => {
    console.log('-----P2 进来了呢');
    setTimeout(() => {
      console.log('P2--------');
      resolve('P22222222');
    }, 500);
  });
};

promiseAll([P1(), P2()])
  .then(responses => {
    responses.forEach(res => {
      console.log(res);
    });
  })
  .catch(err => {
    console.log('-=-=-', err);
  });