css js setInterval
<!DOCTYPE HTML>
<html>
<head>
<style>
#div{
background-color: red;
width:10px;
height:10px;
position:absolute;
}
</style>
</head>
<body>
</body>
<script type="text/javascript" charset="utf-8">
window.onload=function(){
var div=document.createElement("div");
document.body.appendChild(div);
div.id="div";
var x=10,vx =Math.random()*4-2;
var y=10,vy=Math.random()*4-2;
setInterval(function(){
if(x <0||x>300){
vx*=-1;}
if(y <0||y>300){
vy*=-1;
}
x+=vx;
y+=vy;
div.style.left=x+"px";
div.style.top=y+"px";
},17)
}
</script>
</html>
