Merge Sort in TypeScript

merge-sort.ts

function mergeSort(A: number[]): void {
  const n = A.length;
  if (n < 2) {
    return A;
  }
  const mid = Math.floor(n / 2);
  const left = A.slice(0, mid);
  const right = A.slice(mid);
  mergeSort(left);
  mergeSort(right);
  merge(left, right, A);
}

function merge(left: number[], right: number[], A: number[]) {
  let i = 0;
  let j = 0;
  let k = 0;
  while (i < left.length && j < right.length) {
    if (left[i] <= right[j]) {
      A[k] = left[i];
      i++;
    } else {
      A[k] = right[j];
      j++;
    }
    k++;
  }
  while (i < left.length) {
    A[k] = left[i];
    i++;
    k++;
  }

  while (j < right.length) {
    A[k] = right[j];
    j++;
    k++;
  }
}

const A = [2,9,10,2,1,4,-1,0,-9,3,1]
mergeSort(A)
console.log(A)