Shuffle and Return Last 4 Elements

shuffle-and-return-last-4-elements.js

function shuffle(array, amount = undefined) {
  var m = array.length, t, i;

  // While there remain elements to shuffle…
  while (m) {

    // Pick a remaining element…
    i = Math.floor(Math.random() * m--);

    // And swap it with the current element.
    t = array[m];
    array[m] = array[i];
    array[i] = t;
  }
  
  if (amount <= arr.length) {
    return array.slice(-(amount - arr.length))
  }

  return array;
}

// Used like so
var arr = [2, 11, 37, 42];
arr = shuffle(arr, 4)
console.log(arr)

References:
https://bost.ocks.org/mike/shuffle/
https://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array