quicksort.js

  
function quicksort([ ...arr ]) {
  if (!arr.length) {
    return [];
  }
  let left = [], pivot = arr[0], right = [];
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] < pivot) {
      left.push(arr[i]);
    } else {
      right.push(arr[i]);
    }
  }
  return [ ...quicksort(left), pivot, ...quicksort(right) ];
}


function quicksortCheck(array) {
  var sortedArray = array.slice(0); 
  if(sortedArray.length == 0) return [];

  var left = [], right = [], pivot = sortedArray[0];

  for (var i = 1; i < sortedArray.length; i++) {
    if(sortedArray[i] < pivot) {
      left.push(sortedArray[i]);
    } else {
      right.push(sortedArray[i]);
    }
  }

  return [ ...quicksortCheck(left), pivot, ...quicksortCheck(right) ];
}


const arr1 = [ 500, 4, 1, 5, 11, 90, 1100 ];
const arr2 = [ 1, 2, 3, 4 ];
const arr3 = [ 5, 9, 1, 0, 7, 10, 99 ];


console.log(quicksortCheck(arr1), quicksort(arr1));
console.log(quicksortCheck(arr2), quicksort(arr2));
console.log(quicksortCheck(arr3), quicksort(arr3));