Merge Sort in JavaScript

gistfile1.txt

const merge = (arrL, arrR) => {
  const result = [];

  let cursorL = 0;
  let cursorR = 0;

  while (cursorL < arrL.length && cursorR < arrR.length) {
    if (arrL[cursorL] < arrR[cursorR]) {
      result.push(arrL[cursorL++]);
    } else {
      result.push(arrR[cursorR++]);
    }
  }

  return result.concat(arrL.slice(cursorL)).concat(arrR.slice(cursorR));
};

const mergeSort = (arr) => {
  const len = arr.length;

  if (len === 1) {
    return arr;
  }

  const mid = Math.floor(len / 2);
  return merge(mergeSort(arr.slice(0, mid)), mergeSort(arr.slice(mid, len)));
};