返回顶部，只需引入一个js即可

document.write('<div id="k_icopos" class="k_spico"><a href="javascript:void(0)" hidefocus="true" class="k_returntop bb" id="k_returntop" title="返回顶部">&nbsp;</a></div><style>.k_spico {width:50px;height:50px;position:fixed;_position:absolute;display:none;cursor:pointer;}.k_returntop {display:block;width:50px;height:50px;background:url(http://csdnimg.cn/www/images/top_arrow.png) no-repeat 0 0;}.k_returntop:hover {filter:alpha(opacity=60);opacity:0.6;text-decoration:none;}</style>'); function addEvent(obj,type,fn){ if(!obj){return null;} if(obj.addEventListener){ obj.addEventListener(type,function (ev){ var rtn=fn.call(obj,ev); if(rtn==false){ ev.cancelBubble=true; ev.preventDefault(); } },false); }else{ obj.attachEvent('on'+type,function (){ var rtn=fn.call(obj,event); if(rtn==false){ event.cancelBubble=true; return false; } }) } }; function ReturnTop(obj,obj2,num,num2){ if(!obj){return null;} this.obj = document.getElementById(obj); this.obj2 = document.getElementById(obj2); this.bSys = true; this.scrollTop = 0; this.timer = null; this.iSpeed = 0; this.iTop = 0; this.iLeft = 0; this.oBottom = num; this.oWidth = num2; var _this = this; addEvent(window,'scroll',function(){ _this.moveFn(); }) addEvent(window,'resize',function(){ _this.moveFn(); }) } ReturnTop.prototype.moveFn = function(){ var _this = this; var GLOBAlIE6= /msie 6/ig.test(window.navigator.userAgent) && !/msie [1-57-9]/ig.test(window.navigator.userAgent); this.scrollTop = document.documentElement.scrollTop || document.body.scrollTop; this.iTop = document.documentElement.clientHeight-this.oBottom+this.scrollTop; this.iLeft = (document.documentElement.clientWidth-this.oWidth)/2+this.oWidth; if(this.scrollTop>0){ this.obj.style.display = 'block'; this.obj.style.left = this.iLeft + 'px'; if(GLOBAlIE6){ this.obj.style.top = this.iTop + 'px'; if((css(document.body,'backgroundAttachment') !== "fixed") && (css(document.body,'backgroundImage') === "none")){ document.body.style.backgroundRepeat = "no-repeat"; document.body.style.backgroundImage = "url(about:blank)"; document.body.style.backgroundAttachment = "fixed"; } }else { this.obj.style.top = this.iTop-this.scrollTop + 'px'; } }else { this.obj.style.display = 'none'; } if(!this.bSys){ clearInterval(_this.timer); } this.bSys = false; this.obj2.onclick = function(){ _this.topFn(); _this.bSys = false; } } ReturnTop.prototype.topFn = function(){ var _this = this; clearInterval(_this.timer); this.timer = setInterval(function(){ _this.setToFn(); },50) } ReturnTop.prototype.setToFn = function(){ var _this = this; this.iSpeed = Math.floor(-this.scrollTop/8); if(this.scrollTop==0){ clearInterval(_this.timer); } this.bSys = true; document.documentElement.scrollTop = document.body.scrollTop = this.scrollTop + this.iSpeed; } var toTop = new ReturnTop('k_icopos','k_returntop',200,970);