A Rather Easy Way to Implement Quicksort in JavaScript

Don't use in-place swap.

Declare 2 new array left and right (or anything you want to call them). After comparing each element to pivot, push it to left if it's smaller or right if it's bigger than pivot. Then return [...quickSort(left), pivot, ...quickSort(right)] will do the magic.

Of course it's not as good space efficiency-wise, but it's way easier to implement and understand.

Example code:

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