//从上往下滚动

var header_demo = document.getElementById("header_demo");
var header_demo1 = document.getElementById("header_demo1");
var header_demo2 = document.getElementById("header_demo2");
var speed=20;
header_demo2.innerHTML = header_demo1.innerHTML;
header_demo.scrollTop=header_demo.scrollHeight
function Marquee(){
    if(header_demo1.offsetTop-header_demo.scrollTop>=0)
        header_demo.scrollTop+=header_demo2.offsetHeight
    else{
        header_demo.scrollTop--
    }
}
var MyMar = setInterval(Marquee,speed);
header_demo.onmouseover = function(){clearInterval(MyMar)}
header_demo.onmouseout = function(){MyMar = setInterval(Marquee,speed)}

//从右往左滚动
/*
var header_demo = document.getElementById("header_demo");
var header_demo1 = document.getElementById("header_demo1");
var header_demo2 = document.getElementById("header_demo2");
var speed=20;
header_demo2.innerHTML = header_demo1.innerHTML;
function Marquee(){
    if(header_demo2.offsetWidth-header_demo.scrollLeft<=0)
        header_demo.scrollLeft-=header_demo1.offsetWidth
    else{
        header_demo.scrollLeft++
    }
}
var MyMar = setInterval(Marquee,speed);
header_demo.onmouseover = function(){clearInterval(MyMar)}
header_demo.onmouseout = function(){MyMar = setInterval(Marquee,speed)}
*/