sort array - mean calc

gist.js

/**
 * Merge sort - high performance sorting
 */
const mergeSort = (input, field) => {
  const splitted = [];
  for (let i = 0; i < input.length; i++) splitted.push([input[i]]);

  const merged = (function merge(arr) {
    const tempResult = [];
    for (let i = 0; i < arr.length; i += 2) {
      const result = [];
      const current = i;
      const next = i + 1;
      let left = 0;
      let right = 0;

      // for odd arrays, if doesn't has next then it's odd therefore need to push the current array
      if (!arr[next]) tempResult.push(arr[current]);
      else {
        while (left < arr[current].length || right < arr[next].length) {
          // case there's only one element remaining (odd number of elements)
          if (left === arr[current].length && right < arr[next].length) {
            result.push(arr[next][right]);
            right++;
            continue;
          } else if (left < arr[current].length && right === arr[next].length) {
            result.push(arr[current][left]);
            left++;
            continue;
          }

          const val1 = arr[current][left][field];
          const val2 = arr[next][right][field];

          if (val1 < val2) {
            result.push(arr[current][left]);
            left++;
          } else {
            result.push(arr[next][right]);
            right++;
          }
        }
        tempResult.push(result);
      }
    }
    if (tempResult.length > 1) return merge(tempResult);
    else return tempResult;
  })(splitted);

  return merged[0];
}

/**
 * Exception - not a number
 */
function NotANumberException(msg) {
  this.message = msg;
  this.name = 'NotANumberException';
}

/**
 * Calculate mean
 */
const meanCalc = (objList, field) => {
  if(typeof objList !== 'object' || !objList.length) return null;

  let total = 0;
  for (let i = 0; i < objList.length; i++) {
    const item = objList[i];
    if(item.hasOwnProperty(field) && typeof item[field] === 'number')
      total += objList[i][field];
    else
      throw new NotANumberException(`The provided object ${field} for item`, item, 'is not a valid number');
  }
  return total / objList.length;
}


// example:
const a = [
  { name: 'Mr. Burns', age: 145 },
  { name: 'Moe', age: 37 },
  { name: 'Apu', age: 39 },
  { name: 'Carl', age: 34 },
  { name: 'Homer Simpson', age: 38 },
  { name: 'Marge Simpson', age: 36 },
  { name: 'Lisa Simpson', age: 12 },
  { name: 'Bart Simpson', age: 34 },
  { name: 'Maggie Simpson', age: 2 },
  { name: 'Krusty', age: 35 }
];

console.time('mergeSort');
// sort by age
const sortedArray = mergeSort(a, 'age');
console.timeEnd('mergeSort');
console.log(sortedArray);
// calculate mean
console.log('Age mean is: ', meanCalc(sortedArray, 'age'));