_immu = {};

_immu.sample = function(list, n) {

  if (n === undefined) return list.get(_immu.random(list.size - 1));

  return _immu.shuffle(list).slice(0, Math.max(0, n));

};

​

_immu.shuffle = function(list) {

  var set = list;

  var size = set.size;

  var shuffled = Immutable.List(Array(size));

  for (var index = 0, rand; index < size; index++) {

    rand = _immu.random(0, index);

    if (rand !== index) shuffled = shuffled.set(index, shuffled.get(rand));

    shuffled = shuffled.set(rand, set.get(index));

  }

  return shuffled;

};

​

_immu.random = function(min, max) {

  if (max == null) {

    max = min;

    min = 0;

  }

  return min + Math.floor(Math.random() * (max - min + 1));

};

​

var list = Immutable.List([1,2,3,4,5]);

console.log(_immu.sample(list, 3).toJS()); //toJS here is just to show it as an array

​