JS: Merge sort - programming exercise

index.js

const array = [38, 27, 24, 56, 12, 32, 16, 11, 15, 25, 29];
console.log(mergeSort(array));

merge-sort.js

function mergeSort(array) {
  if (array.length <= 1) {
    return array;
  }

  const middle = Math.floor(array.length / 2);
  const left = array.slice(0, middle);
  const right = array.slice(middle);
  return merge(mergeSort(left), mergeSort(right));
}

function merge(left, right) {
  const result = [];
  let lindex = 0;
  let rindex = 0;

  while (lindex < left.length && rindex < right.length) {
    if (left[lindex] < right[rindex]) {
      result.push(left[lindex]);
      lindex++;
    } else {
      result.push(right[rindex]);
      rindex++;
    }
  }

  return [...result, ...left.slice(lindex), ...right.slice(rindex)];
}