Get a random subset of the set

subset.js

var pool = ["1", "2", "3", "4", "5"]
var getRandomSubsets = function (num) { // num: #of elements in the subset
  if (num.length > pool) {
    return null;
  }
  var subPool = {};
  for (var i = 0; i < num; i++) {
    var max = pool.length - 1;
    var min = 0;
    var pick = Math.floor(Math.random() * (max - min + 1)) + min;
    if (pick in subPool) {
      i--;
      continue;
    }
    subPool[pick] = pool[pick];
  }
  return subPool;
}
getRandomSubsets(3);
//eg: return Object {1: "2", 2: "3", 3: "4"}