https://zhidao.baidu.com/question/1859896201945858587.html
https://www.cnblogs.com/playerlife/archive/2012/08/02/2620535.html
https://juejin.im/post/5cc6ee96f265da036706b53f
https://www.jb51.net/article/27971.htm
绑定事件的作用
在openlayers的应用实例：http://linwei.xyz/ol3-primer/ch08/08-05.html