var speed = 30;

demo2.innerHTML = demo1.innerHTML
function Marquee() {
    if (demo2.offsetWidth - demo.scrollLeft <= 0)
        demo.scrollLeft -= demo1.offsetWidth
    else {
        demo.scrollLeft++
    }
}
var MyMar = setInterval(Marquee, speed)
demo.onmouseover = function() { clearInterval(MyMar) }
demo.onmouseout = function() { MyMar = setInterval(Marquee, speed) }