Shuffling arrays

const shuffle = array => {
  // create a clone of the array that we can rearrange in place
  const copy = array.slice()

  // start at the last element, moving towards the front with every repetition
  for (let i = copy.length - 1; i > 0; i--) {
    // get the index of an element left of (and including) the current one
    const j = Math.floor(Math.random() * (i + 1))

    // swap the values at the positions i and j
    const temp = copy[i]
    copy[i] = copy[j]
    copy[j] = temp
  }

  return copy
}

shuffle([1, 2, 3, 4])  // ⇒ [4, 1, 2, 3] (maybe)
shuffle([1, 2, 3, 4])  // ⇒ [3, 1, 2, 4] (maybe)
shuffle([1, 2, 3, 4])  // ⇒ [1, 4, 2, 3] (maybe)
shuffle([1, 2, 3, 4])  // ⇒ [3, 2, 1, 4] (maybe)