index.js

//** jQuery Scroll to Top Control script- (c) Dynamic Drive DHTML code library: http://www.dynamicdrive.com.
//** Available/ usage terms at http://www.dynamicdrive.com (March 30th, 09')
//** v1.1 (April 7th, 09'):
//** 1) Adds ability to scroll to an absolute position (from top of page) or specific element on the page instead.
//** 2) Fixes scroll animation not working in Opera. 


var scrolltotop = {
	//startline: Integer. Number of pixels from top of doc scrollbar is scrolled before showing control
	//scrollto: Keyword (Integer, or "Scroll_to_Element_ID"). How far to scroll document up when control is clicked on (0=top).
	setting: { startline: 100, scrollto: 0, scrollduration: 1000, fadeduration: [500, 100] },
	controlHTML: '', //<img src="assets/img/up.png" style="width:51px; height:42px" /> //HTML for control, which is auto wrapped in DIV w/ ID="topcontrol"
	controlattrs: { offsetx: 5, offsety: 5 }, //offset of control relative to right/ bottom of window corner
	anchorkeyword: '#top', //Enter href value of HTML anchors on the page that should also act as "Scroll Up" links

	state: { isvisible: false, shouldvisible: false },

	scrollup: function () {
		if (!this.cssfixedsupport) //if control is positioned using JavaScript
			this.$control.css({ opacity: 0 }) //hide control immediately after clicking it
		var dest = isNaN(this.setting.scrollto) ? this.setting.scrollto : parseInt(this.setting.scrollto)
		if (typeof dest == "string" && jQuery('#' + dest).length == 1) //check element set by string exists
			dest = jQuery('#' + dest).offset().top
		else
			dest = 0
		this.$body.animate({ scrollTop: dest }, this.setting.scrollduration);
	},

	keepfixed: function () {
		var $window = jQuery(window)
		var controlx = $window.scrollLeft() + $window.width() - this.$control.width() - this.controlattrs.offsetx
		var controly = $window.scrollTop() + $window.height() - this.$control.height() - this.controlattrs.offsety
		this.$control.css({ left: controlx + 'px', top: controly + 'px' })
	},

	togglecontrol: function () {
		var scrolltop = jQuery(window).scrollTop()
		if (!this.cssfixedsupport)
			this.keepfixed()
		this.state.shouldvisible = (scrolltop >= this.setting.startline) ? true : false
		if (this.state.shouldvisible && !this.state.isvisible) {
			this.$control.stop().animate({ opacity: 1 }, this.setting.fadeduration[0])
			this.state.isvisible = true
		}
		else if (this.state.shouldvisible == false && this.state.isvisible) {
			this.$control.stop().animate({ opacity: 0 }, this.setting.fadeduration[1])
			this.state.isvisible = false
		}
	},

	init: function () {
		jQuery(document).ready(function ($) {
			var mainobj = scrolltotop
			var iebrws = document.all
			mainobj.cssfixedsupport = !iebrws || iebrws && document.compatMode == "CSS1Compat" && window.XMLHttpRequest //not IE or IE7+ browsers in standards mode
			mainobj.$body = (window.opera) ? (document.compatMode == "CSS1Compat" ? $('html') : $('body')) : $('html,body')
			mainobj.$control = $('<div id="topcontrol">' + mainobj.controlHTML + '</div>')
				.css({ position: mainobj.cssfixedsupport ? 'fixed' : 'absolute', bottom: mainobj.controlattrs.offsety, right: mainobj.controlattrs.offsetx, opacity: 0, cursor: 'pointer' })
				.attr({ title: 'Scroll Back to Top' })
				.click(function () { mainobj.scrollup(); return false })
				.appendTo('body')
			if (document.all && !window.XMLHttpRequest && mainobj.$control.text() != '') //loose check for IE6 and below, plus whether control contains any text
				mainobj.$control.css({ width: mainobj.$control.width() }) //IE6- seems to require an explicit width on a DIV containing text
			mainobj.togglecontrol()
			$('a[href="' + mainobj.anchorkeyword + '"]').click(function () {
				mainobj.scrollup()
				return false
			})
			$(window).bind('scroll resize', function (e) {
				mainobj.togglecontrol()
			})
		})
	}
}

scrolltotop.init()