向下滚动浏览器,体验返回顶部

新建一个 JS文件,并写入以下代码
var scrolltotop={
    setting:{
        startline:100, 
        scrollto:0,
        scrollduration:400, 
        fadeduration:[500,100]
    },
    controlHTML:'<img src="topback.gif" style="width:54px; height:54px; border:0;" />',
    controlattrs:{offsetx:30,offsety:80},
    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();