function $(id) {
    return typeof id == "string" ? document.getElementById(id) : id;
};
function Roller(sId, iDelay, iSpeed, iheight){
    var rollBox = $(sId);
	var iDelay = iDelay||2000;//每次停顿事件。
	var iSpeed=iSpeed||50;//滚动速度。
	var iheight = iheight||20;//容器高度
	var timer = null, pause = false;
	
	var start = function(){
		timer = setInterval(rollUp,iSpeed);
	}
	
	var rollUp = function(){
		if(pause){ return;}
		    rollBox.scrollTop += 2;
			if(rollBox.scrollTop % iheight == 0){
				clearInterval(timer);
				rollBox.appendChild(rollBox.getElementsByTagName('li')[0]);
				rollBox.scrollTop=0;
				setTimeout(start,iDelay);
			}
	}
  
    rollBox.onmouseover = function(){pause = true;}
	rollBox.onmouseout = function(){pause = false;}
  
    setTimeout(start,iDelay);
}
window.onload = function(){
Roller('rollBox', 2000, 50, 20)
}