Javascript Array numberCombinations()

Array.prototype.numberCombinations = function(){
  var fn = function(active, remaining, combinations) {
    if (!active && !remaining.length){
      return;//from ww  w  .  j  a v  a 2 s. com
    }
    if (!remaining.length) {
      combinations.push(active.split('').map(function(combo){ return parseInt(combo,10) }));
    } else {
      fn(active + remaining[0], remaining.slice(1), combinations);
      fn(active, remaining.slice(1), combinations);
    }
    return combinations;
  }
  return fn("", this, []);
}