chaser_test.js

const mergeSortObj = (arr, param) => {
  if (arr.length < 2)
    return arr;

  const middle = parseInt(arr.length / 2);
  const [left, right] = [arr.slice(0, middle), arr.slice(middle, arr.length)]

  return mergeObj(mergeSortObj(left, param), mergeSortObj(right, param), param);
}

const mergeObj = (leftArr, rightArr, param) => {
  const result = [];

  while (leftArr.length && rightArr.length) {
    if (leftArr[0][param] <= rightArr[0][param]) {
      result.push(leftArr.shift());
    } else {
      result.push(rightArr.shift());
    }
  }

  while (leftArr.length)
  result.push(leftArr.shift());

  while (rightArr.length)
  result.push(rightArr.shift());

  return result;
}

const avgObj = (arr, param) => {
  const length = arr.length

  return arr.reduce((acc, val) => {
    return acc + val[param] / length;
  }, 0);
}