iterator.js

var agg = (function(){
    var index = 0,
        data = [1, 2, 3, 4, 5],
        length = data.length;

    return {
        next: function(){
            var element;
            if(!this.hasNext()){
                return null;
            }
            element = data[index];
            index = index + 1;
            return element;
        },

        hasNext: function(){
            return index < length;
        }
    }
}());

while(agg.hasNext()){
  console.log(agg.next());
}