function stopdefault(e) {// 禁止浏览器默认行为

	var e= e || event;

	if (e.preventdefault) {

		e.preventdefault();

	} else {

		e.returnvalue = false;

	}

}



//模拟滚动条

function imitatescroll(scrollbox, scrollobj, scrollbar, scrollbtn)

{//scrollbox被滚动对象外框，scrollobj被滚动对象，scrollbar滚动条块，滚动条按钮

	this.init(scrollbox, scrollobj, scrollbar, scrollbtn);

}



imitatescroll.prototype = {

	scale:function() {//被滚动对象与被滚动对象外框的高度比例计算

		return (this.scrollobj.scrollheight/this.scrollbox.clientheight);

	},

	scrollbtnmousedown:function(ev) {//滚动按钮按下

		var _this = this;

		var disy = ev.clienty - this.scrollbtn.offsettop;//鼠标y坐标距离滚动按钮头部的距离

		var maxtop =  this.scrollbar.clientheight - this.scrollbtn.offsetheight;



		document.onmousemove = function(ev) {

			if (document.all) {//ie 禁止选择

				document.body.onselectstart = new function("return false");

			} else {// chrome, ff

				document.body.classname = "chromeonselectstart";

			}



			var oevent = ev || event;

			var t = oevent.clienty - disy;

			t = t>maxtop ? maxtop : t;

			t = t<0 ? 0 : t;



			 _this.scrollbtn.style.top = t + "px";

			 //_this.scrollobj.style.top = -t / _this.scrollbar.clientheight * _this.scrollobj.scrollheight + "px";

			  _this.scrollobj.style.top = -t / (_this.scrollbar.clientheight-_this.scrollbtn.offsetheight) * (_this.scrollobj.scrollheight-_this.scrollbox.clientheight) + "px";

		};

		document.onmouseup = function() {

			if (document.all) {//ie 解除禁止选择

				document.body.onselectstart = new function("return true");

			} else {// chrome, ff

				document.body.classname = "";

			}



			document.onmousemove = document.onmouseup = null;//清除move和up事件

		};

	},

	scrollboxmousewheel:function(ev) {//鼠标滚轮滚动

		var direct = 0;

		var topcur = this.scrollbtn.offsettop;

		var maxtop =  this.scrollbar.clientheight - this.scrollbtn.offsetheight;

		//滚轮每次滚动，滚动按钮该走的距离，测试chrome滚8次差不多一屏

		var directtop = this.scrollbox.clientheight / 8 / this.scrollobj.scrollheight * this.scrollbar.clientheight;

		directtop = directtop>0 ? math.ceil(directtop) : math.floor(directtop);



		stopdefault(ev);//禁止浏览器自身的滚动条滚动效果

		if (ev.wheeldelta)  {//ie/opera/chrome 

			direct = ev.wheeldelta;

		} else if (ev.detail) {//firefox 

			direct = ev.detail * (-1);

		}



		if(parsefloat(direct) > 0) {

			var topend = topcur - directtop;

			if (topend < 0) {topend = 0;}

		} else {

			var topend = topcur + directtop;

			topend = topend>maxtop ? maxtop : topend;

		}



		this.scrollbtn.style.top = topend + "px";

		//this.scrollobj.style.top = -topend / this.scrollbar.clientheight * this.scrollobj.scrollheight + "px";

		this.scrollobj.style.top = -topend / (this.scrollbar.clientheight-this.scrollbtn.offsetheight) * (this.scrollobj.scrollheight-this.scrollbox.clientheight) + "px";

	},

	init:function(scrollbox, scrollobj, scrollbar, scrollbtn) {//初始化

		this.scrollbox = typeof scrollbox == "string" ? document.getelementbyid(scrollbox) : scrollbox;

		this.scrollobj = typeof scrollobj == "string" ? document.getelementbyid(scrollobj) : scrollobj;

		this.scrollbar = typeof scrollbar == "string" ? document.getelementbyid(scrollbar) : scrollbar;

		this.scrollbtn = typeof scrollbtn == "string" ? document.getelementbyid(scrollbtn) : scrollbtn;

		var scale = this.scale();////被滚动对象与被滚动对象外框的高度比例



		if (scale <= 1) {//判断是否达到产生滚动条的条件

			this.scrollbar.style.display = "none";

			return;

		} else {

			this.scrollbar.style.display = "block";

		}

		// if(_this.scrollobj.scrollheight+_this.scrollobj.offsettop < _this.scrollbox.clientheight)

		// {//判断被滚动对象是否滚过头了

		// 	 _this.scrollobj.style.top = _this.scrollbox.clientheight-_this.scrollobj.scrollheight+"px";

		// }



		//初始化滚动按钮的高度和top值

		//this.scrollbtn.style.height = 20 + "px"; //设定滚动按钮的高度

		//this.scrollbtn.style.top = -this.scrollobj.offsettop/this.scrollobj.scrollheight*this.scrollbar.clientheight + "px";



		var _this = this;

		this.scrollbtn.onmousedown = function(e) {//滚动按钮拖拽事件

			var e = e || event;

			_this.scrollbtnmousedown(e);

		};



		//绑定滚轮事件

		if (this.scrollbox.addeventlistener) {//ff3.5以下

			this.scrollbox.addeventlistener("dommousescroll", function(e) {

				var e = e || event;

				_this.scrollboxmousewheel(e)

			}, false);

		}

		//w3c

		this.scrollbox.onmousewheel = function(e) {

			var e = e || event;

			_this.scrollboxmousewheel(e)

		}; //ie/opera/chrome

	}

}