var speed = 20; //数字越大速度越慢
            var tab = document.getElementById("demo");
            var tab1 = document.getElementById("demo1");
            var tab2 = document.getElementById("demo2");
            tab2.innerHTML = tab1.innerHTML;
            function Marquee() {
                if (tab2.offsetWidth - tab.scrollLeft <= 0)
                    tab.scrollLeft -= tab1.offsetWidth
                else {
                    tab.scrollLeft++;
                }
            }
            var MyMar = setInterval(Marquee, speed);
            tab.onmouseover = function() { clearInterval(MyMar) };
            tab.onmouseout = function() { MyMar = setInterval(Marquee, speed) };