Quick sort in javascript

quicksort.js

function arr_union(arr1, arr2) {
  return arr1.concat(arr2);
}

function quicksort(array) {
  let pivot = 0;
  let compared = array.length - 1;

  if (array.length <= 1) return array;

  while (true) {
    if (array[pivot] > array[compared]) {
      if (compared > pivot) {
        [array[pivot], array[compared]] =  [array[compared], array[pivot]]; // swaping
        [pivot, compared] = [compared, pivot + 1]; // swaping but compared = pivot + 1
      } else compared += 1;
    } else if (array[pivot] < array[compared]){
      if (pivot > compared) {
        [array[pivot], array[compared]] =  [array[compared], array[pivot]]; // swaping
        [pivot, compared] = [compared, pivot - 1]; // swaping but compared = pivot - 1
      } else compared -= 1;
    } else {
      if (pivot > compared) compared += 1;
      else if (compared > pivot) compared -= 1;
    }

    if (compared == pivot) break;
  }

  // if array[0] is already the smallest number
  if (pivot === 0) return arr_union(array.slice(0, 1), quicksort(array.slice(1)));
  // and if it's not the smallest
  else return arr_union(quicksort(array.slice(0, pivot)), quicksort(array.slice(pivot)));
}