var o_demo=document.getElementById('demo');
  var o_demo1=document.getElementById('demo1');
  var o_demo2=document.getElementById('demo2');
  var speed1=100;
   o_demo2.innerHTML=o_demo1.innerHTML; //克隆demo1为demo2
   function Marquee1(){
		//当滚动至demo1与demo2交界时
		if(o_demo2.offsetHeight-o_demo.scrollTop<=0)
			o_demo.scrollTop-=o_demo1.offsetHeight; //demo跳到最顶端
			else{
			o_demo.scrollTop++;
		 }
   }
   var MyMar1=setInterval(Marquee1,speed1);//设置定时器
//鼠标移上时清除定时器达到滚动停止的目的
   o_demo.onmouseover=function() {
	   clearInterval(MyMar1);
	   }
//鼠标移开时重设定时器
   o_demo.onmouseout=function(){
	   MyMar1=setInterval(Marquee1,speed1);
	}