迭代器模式

iterator.js

var element;

while (element = agg.next()) {
  // do something with the element
  console.log(element);
}

// use hasNext()
while (agg.hasNext()) {
  // do something with the next element...
  console.log(agg.next());
}

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 + 2;
      return element;
    },
    hasNext: function() {
      return index < length;
    },
    rewind: function() {
      index = 0;
    },
    current: function() {
      return data[index];
    }
  };
}());

// this loop logs 1, then 3, then 5
while (agg.hasNext()) {
  console.log(agg.next());
}

// go back
agg.rewind();
console.log(agg.current()); // 1