mergeSort.js

/**
 * Simple mergesort exercise
 */

const mergeSort = unsortedArray => {
  if (unsortedArray.length <= 1) return unsortedArray;
  const middle = Math.floor(unsortedArray.length / 2);
  const left = unsortedArray.slice(0, middle);
  const right = unsortedArray.slice(middle);
  return merge(mergeSort(left), mergeSort(right));
};

const merge = (left, right) => {
  const resultArray = [];
  let leftIndex = 0;
  let rightIndex = 0;

  while (leftIndex < left.length && rightIndex < right.length) {
    if (left[leftIndex] < right[rightIndex]) {
      resultArray.push(left[leftIndex]);
      leftIndex++;
    } else {
      resultArray.push(right[rightIndex]);
      rightIndex++;
    }
  }
  return [
    ...resultArray,
    ...left.slice(leftIndex),
    ...right.slice([rightIndex])
  ];
};

const array = [10, -1, 2, 5, 0, 6, 4, -5];
const array2 = ["TJ", "Melissa", "Figs", "Autumn", "Mooch"];

console.log("mergeSort(array): ", mergeSort(array));
// console.log("mergeSort(array2): ", mergeSort(array2));