Knuth shuffle

shuffle.js

// Implementation of Knuth shuffle: http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
// More implementations: http://stackoverflow.com/questions/6274339/how-can-i-shuffle-an-array-in-javascript
var shuffle = function(a) {
  for (var i = a.length; --i > 0;) {
    // Get random number between first and current index.
    var r = Math.floor(Math.random() * (i + 1));
    // Swap random with current index values.
    var d = a[r];
    a[r] = a[i];
    a[i] = d;
  }
  return a;
}