Javascript Array swap(firstIndex, secondIndex)

function bubbleSort(arr) {
  if (arr.length === 0 || arr.length === undefined) {
    return "No array as arg!"
  }// ww w.  j av a  2s.c om

  if (arr.length === 1) {
    return arr;
  }

  var swapped = true;

  while (swapped) {
    swapped = false;
    for (let i = 0; i < arr.length; i++) {
      if (arr[i] > arr[i+1]) {
      //   let temp = arr[i];
      //   arr[i] = arr[i+1];
      //   arr[i+1] = temp;
        arr = arr.swap(arr[i],arr[i+1])// arr.swap(arr[i], arr[i+1])
        swapped = true;
      }
    }
  }

  return arr;

}

Array.prototype.swap = function(firstIndex, secondIndex) {
  let temp = firstIndex;
  this[firstIndex] = this[secondIndex];
  this[secondIndex] = this[temp];
}

console.log(bubbleSort([8,7,3,2,5,1]));