http://www.zhangxinxu.com/wordpress/2013/12/javascript-js-%E5%85%83%E7%B4%A0-%E6%8A%9B%E7%89%A9%E7%BA%BF-%E8%BF%90%E5%8A%A8-%E5%8A%A8%E7%94%BB/
