quicksort.js

function q(a){
  if(a.length <= 1) return a
  let p = a.shift()  //or pop
  let left = a.filter(e => e <= p) // or in one interation
  let right = a.filter(e => e > p)
  return [...q(left), p, ...q(right)]
}

console.log(q([2,6,7,1,4,9,3,5]))