js代码

<script type="text/javascript">
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:'<img src="images/top.png" style="width:30px; height:30px; border:0;" />', //返回顶部按钮
	controlattrs:{offsetx:10,offsety:10},//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="'+mainobj.anchorkeyword+'"]').click(function(){mainobj.scrollup();return false;});
			$(window).bind("scroll resize",function(e){mainobj.togglecontrol();});
		});
	}
};
scrolltotop.init();
</script>