左右不断循环滚动

//左右不断循环滚动
var splep=30;
demo2.innerHTML=demo1.innerHTML;
var _left = demo1.offsetWidth;
var mymarq=setInterval(marquee,splep);
demo.onmouseover=function(){ clearInterval(mymarq);}
demo.onmouseout=function(){ mymarq=setInterval(marquee,splep);}
function marquee(){
    if((_left - demo.scrollLeft) <= 0){
        demo.scrollLeft = 0;
    }else{
        ++demo.scrollLeft;
    }
}