https://www.casertafocus.net/home/media/plg_system_topofthepage/ScrollSpy.min.js

1/*
2---
3description:     ScrollSpy
4
5authors:
6  - David Walsh (http://davidwalsh.name)
7
8license:
9  - MIT-style license
10
11requires:
12  core/1.2.1:   '*'
13
14provides:
15  - ScrollSpy
16...
17*/
18var ScrollSpy=new Class({Implements:[Options,Events],options:{container:window,max:0,min:0,mode:"vertical"},initialize:function(a){this.setOptions(a);this.container=document.id(this.options.container);this.enters=this.leaves=0;this.inside=false;this.listener=function(d){var b=this.container.getScroll(),c=b[this.options.mode=="vertical"?"y":"x"];if(c>=this.options.min&&(this.options.max==0||c<=this.options.max)){if(!this.inside){this.inside=true;this.enters++;this.fireEvent("enter",[b,this.enters,d])}this.fireEvent("tick",[b,this.inside,this.enters,this.leaves,d])}else{if(this.inside){this.inside=false;this.leaves++;this.fireEvent("leave",[b,this.leaves,d])}}this.fireEvent("scroll",[b,this.inside,this.enters,this.leaves,d])};this.addListener()},start:function(){this.container.addEvent("scroll",this.listener.bind(this))},stop:function(){this.container.removeEvent("scroll",this.listener.bind(this))},addListener:function(){this.start()}});