迭代器模式

提供一个API来遍历或者操纵复杂的自定义数据结构

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;
        }
    }

}());

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