jquery.scrollfire

Allows useful callbacks to be fired upon elements scrolling into and out of view from both the top and bottom of the viewport/window.

https://cdnjs.webstatic.cn/ajax/libs/jquery.scrollfire/1.4.0/jquery.scrollfire.js
https://cdnjs.webstatic.cn/ajax/libs/jquery.scrollfire/1.4.0/jquery.scrollfire.min.js