Shuffle an Array and Return a New One in JS

Question

I want to know how to shuffle an array and return a NEW array. So far I have seen this solution in Stack Overflow:

How to randomize (shuffle) a JavaScript array?

This solution works perfectly in returning the same array shuffled, but I don't really understand why. Can anyone explain this and help me revise it so that it returns a new array?

Thanks!

Answer 1

The easiest way I know of to create a copy of an array is using:

var newArray = [].concat(originalArray);

You could perform that in the first line of most of the solutions on the linked answer and you would be getting a new array back with the original untouched. Here is a modified version of the top rated answer on the linked question:

function shuffle(originalArray) {
  var array = [].concat(originalArray);
  var currentIndex = array.length, temporaryValue, randomIndex;

  // While there remain elements to shuffle...
  while (0 !== currentIndex) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex -= 1;

    // And swap it with the current element.
    temporaryValue = array[currentIndex];
    array[currentIndex] = array[randomIndex];
    array[randomIndex] = temporaryValue;
  }

  return array;
}