An example of how to maintain state with closures

iterator.js

function create_iterator(list){
  var index = 0;
  return function(){
    if(index == list.length){
      return false;
    }else{
      return list[index++];
    }
  }
}

var list = [1, 1, 2, 3, 5, 8, 13, 21];
var iterator = create_iterator(list);
while(value = iterator()){
  console.log(value);
}