Write a JavaScript program to find the kth greatest element of a given array of integers

function Kth_greatest_in_array(arr, k) {

  for (var i = 0; i < k; i++) {
    var max_index = i,
      tmp = arr[i];

    for (var j = i + 1; j < arr.length; j++) {
      if (arr[j] > arr[max_index]) {
        max_index = j;
      }
    }

    arr[i] = arr[max_index];
    arr[max_index] = tmp;
  }

  return arr[k - 1];
}

console.log(Kth_greatest_in_array([1,2,6,4,5], 3))
console.log(Kth_greatest_in_array([-10,-25,-47,-36,0], 1))