<style>.up{width:54px;height:54px;background:url(/Images/topback.gif) no-repeat 0 0;filter:alpha(Opacity=60);-moz-opacity:0.6;opacity: 0.6;}.up:hover{filter:alpha(Opacity=100);-moz-opacity:1;opacity:1;}</style>

var scrolltotop={	setting:{		startline:100, //起始行		scrollto:0, //滚动到指定位置		scrollduration:400, //滚动过渡时间		fadeduration:[500,100] //淡出淡现消失	},	controlHTML:‘<div class="up"></div>‘, //返回顶部按钮	controlattrs:{offsetx:30,offsety:80},//返回按钮固定位置	anchorkeyword:"#top",	state:{		isvisible:false,		shouldvisible:false	},scrollup:function(){		if(!this.cssfixedsupport){			this.$control.css({opacity:0});		}		var dest=isNaN(this.setting.scrollto)?this.setting.scrollto:parseInt(this.setting.scrollto);		if(typeof dest=="string"&&jQuery("#"+dest).length==1){			dest=jQuery("#"+dest).offset().top;		}else{			dest=0;		}		this.$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($){			var mainobj=scrolltotop;			var iebrws=document.all;			mainobj.cssfixedsupport=!iebrws||iebrws&&document.compatMode=="CSS1Compat"&&window.XMLHttpRequest;			mainobj.$body=(window.opera)?(document.compatMode=="CSS1Compat"?$("html"):$("body")):$("html,body");			mainobj.$control=$(‘<div id="topcontrol">‘+mainobj.controlHTML+"</div>").css({position:mainobj.cssfixedsupport?"fixed":"absolute",bottom:mainobj.controlattrs.offsety,right:mainobj.controlattrs.offsetx,opacity:0,cursor:"pointer"}).attr({title:"返回顶部"}).click(function(){mainobj.scrollup();return false;}).appendTo("body");if(document.all&&!window.XMLHttpRequest&&mainobj.$control.text()!=""){mainobj.$control.css({width:mainobj.$control.width()});}mainobj.togglecontrol();			$(‘a[href="http://www.mamicode.com/‘+mainobj.anchorkeyword+‘"]‘).click(function(){mainobj.scrollup();return false;});			$(window).bind("scroll resize",function(e){mainobj.togglecontrol();});		});	}};scrolltotop.init();