var getTime = (function() {
  var startTime = Date.now();
  return function() {
    return (Date.now() - startTime) / 1000;
  };
})();
Array.prototype.asyncMapP = function(callback) {
  return Promise.all(this.map(callback));
};
Array.prototype.asyncMapS = async function(callback) {
  var res = [];
  for (var i = 0; i < this.length; i++) {
    res.push(await callback(this[i], i, this));
  }
  return res;
};

function getSquare(i, j, arr) {
  console.log(`executing getSquare at ${getTime()}`);
  return i * i;
}
function getSquareAsync(i, j, arr) {
  return new Promise(resolve =>
    setTimeout(() => {
      console.log(`executing getSquareAsync at ${getTime()}`);
      resolve(i * i);
    }, 2000)
  );
}

async function run() {
  var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  var result1 = arr.map(getSquare);
  console.log(`result1 @ ${getTime()}`, result1);
  // result1 is [ 1, 4, 9, 16, 25, 36, 49, 64, 81, 100 ]
  var result2 = await arr.asyncMapP(getSquareAsync);
  console.log(`result2 @ ${getTime()}`, result2);
  // result2 is [ 1, 4, 9, 16, 25, 36, 49, 64, 81, 100 ]
  var result3 = await arr.asyncMapS(getSquareAsync);
  console.log(`result3 @ ${getTime()}`, result3);
  // result3 is [ 1, 4, 9, 16, 25, 36, 49, 64, 81, 100 ]
}

run();