<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>018</title>
<style type="text/css">
#elem
{
width: 600px;
height: 400px;
border: 1px solid black;
}
</style>
<script type="text/javascript">
window.onload = window.onresize = function(){
var box = document.getElementById('elem');
var style = window.getComputedStyle(box,null);
var height = parseInt(style.getPropertyValue("height"));
var width = parseInt(style.getPropertyValue("width"));
var x = width/2;
var y = height/2;
var circleRadius = Math.min(width, height)/2;
var circ = document.getElementById("circ");
circ.setAttribute("r", circleRadius);
circ.setAttribute("cx", x);
circ.setAttribute("cy", y);
}
</script>
</head>
<body>
<div id="elem">
<svg width="100%" height="100%">
<circle id="circ" width="10" height="10" r="10" fill="red"></circle>
</svg>
</div>
</body>
</html>
