https://www.justinvass.com.au/jsfiles/scrolltopcontrol.js

1var width_val;
2
3if( typeof( window.innerWidth ) != 'undefined' ) {
4    //Non-IE
5    width_val = window.innerWidth;
6  } else {
7    width_val = screen.width;
8  }
9
10if(width_val > 980){
11//	alert(width_val);
12var width_fix1 = (width_val - 980) / 2;
13var width_fix = (width_fix1 + 215)-9;
14}
15else {
16	width_fix = 215;
17}
18
19
20
21var scrolltotop={
22	//startline: Integer. Number of pixels from top of doc scrollbar is scrolled before showing control
23	//scrollto: Keyword (Integer, or "Scroll_to_Element_ID"). How far to scroll document up when control is clicked on (0=top).
24	setting: {startline:200, scrollto: 0, scrollduration:1000, fadeduration:[1000, 100]},
25	controlHTML: '<img src="images/top.gif" style="width:21px; height:26px" />', //HTML for control, which is auto wrapped in DIV w/ ID="topcontrol"
26	controlattrs: {offsetx:width_fix, offsety:85}, //offset of control relative to right/ bottom of window corner
27	anchorkeyword: '#top', //Enter href value of HTML anchors on the page that should also act as "Scroll Up" links
28
29	state: {isvisible:false, shouldvisible:false},
30
31	scrollup:function(){
32		if (!this.cssfixedsupport) //if control is positioned using JavaScript
33			this.$control.css({opacity:0}) //hide control immediately after clicking it
34		var dest=isNaN(this.setting.scrollto)? this.setting.scrollto : parseInt(this.setting.scrollto)
35		if (typeof dest=="string" && jQuery('#'+dest).length==1) //check element set by string exists
36			dest=jQuery('#'+dest).offset().top
37		else
38			dest=0
39		this.$body.animate({scrollTop: dest}, this.setting.scrollduration);
40	},
41
42	keepfixed:function(){
43		var $window=jQuery(window)
44		var controlx=$window.scrollLeft() + $window.width() - this.$control.width() - this.controlattrs.offsetx
45		var controly=$window.scrollTop() + $window.height() - this.$control.height() - this.controlattrs.offsety
46		this.$control.css({left:controlx+'px', top:controly+'px'})
47	},
48
49	togglecontrol:function(){
50		var scrolltop=jQuery(window).scrollTop()
51		if (!this.cssfixedsupport)
52			this.keepfixed()
53		this.state.shouldvisible=(scrolltop>=this.setting.startline)? true : false
54		if (this.state.shouldvisible && !this.state.isvisible){
55			this.$control.stop().animate({opacity:1}, this.setting.fadeduration[0])
56			this.state.isvisible=true
57		}
58		else if (this.state.shouldvisible==false && this.state.isvisible){
59			this.$control.stop().animate({opacity:0}

59, this.setting.fadeduration[1])
60			this.state.isvisible=false
61		}
62	},
63	
64	init:function(){
65		jQuery(document).ready(function($){
66			var mainobj=scrolltotop
67			var iebrws=document.all
68			mainobj.cssfixedsupport=!iebrws || iebrws && document.compatMode=="CSS1Compat" && window.XMLHttpRequest //not IE or IE7+ browsers in standards mode
69			mainobj.$body=(window.opera)? (document.compatMode=="CSS1Compat"? $('html') : $('body')) : $('html,body')
70			mainobj.$control=$('<div id="topcontrol">'+mainobj.controlHTML+'</div>')
71				.css({position:mainobj.cssfixedsupport? 'fixed' : 'absolute', bottom:mainobj.controlattrs.offsety, right:mainobj.controlattrs.offsetx, opacity:0, cursor:'pointer'})
72				.attr({title:'Scroll Back to Top'})
73				.click(function(){mainobj.scrollup(); return false})
74				.appendTo('body')
75			if (document.all && !window.XMLHttpRequest && mainobj.$control.text()!='') //loose check for IE6 and below, plus whether control contains any text
76				mainobj.$control.css({width:mainobj.$control.width()}) //IE6- seems to require an explicit width on a DIV containing text
77			mainobj.togglecontrol()
78			$('a[href="' + mainobj.anchorkeyword +'"]').click(function(){
79				mainobj.scrollup()
80				return false
81			})
82			$(window).bind('scroll resize', function(e){
83				mainobj.togglecontrol()
84			})
85		})
86	}
87}
88
89scrolltotop.init()