i % j === 0

function fn() {
  const arr = []
  for (let i = 2; i <= 100; i++) {
    let bl = false
    for (let j = 2; j <= i; j++) {
      if (i === j) continue
      i % j === 0 && (bl = true)
    }
    !bl && arr.push(i)
  }
  return arr
}
console.log(fn()) 

function qSort(arr) {
  if (arr.length <= 1) return arr
  const index = Math.floor(arr.length / 2)
  const midVal = arr.splice(index, 1)[0]
  const left = [],
    right = []
  arr.forEach(item => {
    if (item < midVal) left.push(item)
    else right.push(item)
  })
  return [...qSort(left), midVal, ...qSort(right)]
}
qSort([2, 5, 8, 9, 3])