function bsr(arr, m) {
  let l = 0;
  let r = arr.length - 1;


  while (l <= r) {
    const mid = (l + (r - l) / 2) | 0;
    const val = arr[mid];

    if (val === m) return mid;
    if (m > val) l = mid + 1;
    if (m < val) r = mid - 1;
  }

  return -1;
}

a = [1, 2, 3, 4, 5, 6, 7, 8, 10, 12];
b = 3;

bsr(a, b);