test.svg

<svg width="100%" height="100%" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
	<script type="text/javascript">
	// <![CDATA[
	function change(evt) {
		var target = evt.target;
		var radius = target.getAttribute("r");
		radius = (radius == 15) ? 45 : 15
		target.setAttribute("r", radius);
	}
	// ]]>
	</script>

	<circle cx="50" cy="50" r="45" fill="green" onclick="change(evt)" />
</svg>