quick-sort.js

function quickSort(array) {

  if (array.length < 1) {
    return [];
  }

  var left = [];
  var right = [];
  var pivot = array[0];

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

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

console.log(quickSort([4, 9, 2, 1, 6, 3, 8])); // [1,2,3,4,6,8,9]