It appears that all of the JavaScript must be included inside of the SVG for it to run. I was unable to reference any external function, or libraries. This meant that your code was breaking at svgstyle = svgobj.getStyle();
This will do what you are attempting.
<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns='http://www.w3.org/2000/svg' version='1.1' height='600' width='820'>
<script type="text/ecmascript"><![CDATA[
function changerect(evt) {
var svgobj=evt.target;
svgobj.style.opacity= 0.3;
svgobj.setAttribute ('x', 300);
}
]]>
</script>
<rect onclick='changerect(evt)' style='fill:blue;opacity:1' x='10' y='30' width='100'height='100' />
</svg>
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…