<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
body{
margin: 0;
padding: 0;
}
#circle{
position: relative;
width: 300px;
height: 300px;
background: #f2f2f2;
border-radius: 50%;
}
#ball{
position: absolute;
width: 10px;
height: 10px;
margin-left: -5px;
margin-top: -5px;
background: red;
border-radius: 50%;
}
</style>
</head>
<body>
<div id="circle">
<div id="ball"></div>
</div>
<script type="text/javascript">
var oCircle = document.getElementById("circle");
var oBall = document.getElementById("ball");
var r = oCircle.offsetWidth/2;
var angle = 0;
var timer = setInterval(function(){
angle++;
var hd = Math.PI/180*angle;
var x = r*Math.cos(hd);
var y = r*Math.sin(hd);
oBall.style.left =r+ x + "px";
oBall.style.top =r- y + "px";
},30)
</script>
</body>
</html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
body{
margin: 0;
padding: 0;
}
#circle{
position: relative;
width: 300px;
height: 300px;
background: #f2f2f2;
border-radius: 50%;
}
#ball{
position: absolute;
width: 10px;
height: 10px;
margin-left: -5px;
margin-top: -5px;
background: red;
border-radius: 50%;
}
</style>
</head>
<body>
<div id="circle">
<div id="ball"></div>
</div>
<script type="text/javascript">
var oCircle = document.getElementById("circle");
var oBall = document.getElementById("ball");
var r = oCircle.offsetWidth/2;
var angle = 0;
var timer = setInterval(function(){
angle++;
var hd = Math.PI/180*angle;
var x = r*Math.cos(hd);
var y = r*Math.sin(hd);
oBall.style.left =r+ x + "px";
oBall.style.top =r- y + "px";
},30)
</script>
</body>
</html>