动态获取元素的属性值

这里引入相关的4条博客，与我们讲的实例有关

https://www.haorooms.com/post/jquery_offset_xy

https://www.cnblogs.com/goloving/p/7113567.html

http://www.cnblogs.com/anniey/p/6591079.html

https://blog.csdn.net/linbooooo1987/article/details/17464725