stepik-async-homework.js

function parallel(arr, callback) {
  const promises = arr.map(func => {
    return new Promise((resolve, reject) => {
      const next = (err, data) => err ? reject(err) : resolve(data);
      func(next);
    });
  });

  Promise
    .all(promises)
    .then(result => callback(null, result))
    .catch(err => callback(err));
}


// Пример использования:

function createAsyncFunction(ms) {
  return function(callback) {
    setTimeout(() => callback(null, ms), ms);
  }
}

function createAsyncThrowErrorFunction() {
  return function (callback) {
    callback(new Error('23'));
  }
}

parallel(
  [
    createAsyncFunction(5000),
    createAsyncFunction(3000),
    createAsyncThrowErrorFunction()
  ],
  function(err, result) {
    console.log(err, result);
  }
);