Shuffle a JavaScript array

shuffle.js

Array.prototype.shuffle = function () {
  var copy = this.concat()
  var currentIndex = copy.length
  
  while (currentIndex !== 0) {
    let randomIndex = Math.floor(currentIndex * Math.random())
    currentIndex--

    let temp = copy[currentIndex]
    copy[currentIndex] = copy[randomIndex]
    copy[randomIndex] = temp
  }
  
  return copy
}