var demo = document.getElementById("product_show");
var demo1 = document.getElementById("demo1");
var demo2 = document.getElementById("demo2");
var speed=1;    //数值越大滚动速度越慢
function MarqueeLeft () {
if(demo2.offsetWidth-demo.scrollLeft<=0)
demo.scrollLeft-=demo1.offsetWidth;
else{
demo.scrollLeft++;
}
}
function MarqueeRight () {
if(demo.scrollLeft<=0)
demo.scrollLeft+=demo2.offsetWidth;
else{
demo.scrollLeft--;
}
}
var MyMar;
leftArrow.onmouseout = function(){
clearInterval(MyMar);}
leftArrow.onmouseover = function(){
MyMar = setInterval(MarqueeLeft,speed);}
rightArrow.onmouseout = function(){
clearInterval(MyMar);}
rightArrow.onmouseover = function(){
MyMar = setInterval(MarqueeRight,speed);
}