JS - Change Body Image based on URL

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Banner Test</title>
<script type="text/javascript">
function getParam ( sname )
{
  var params = location.search.substr(location.search.indexOf("?")+1);
  var sval = "";
  params = params.split("&");
    // split param and value into individual pieces
    for (var i=0; i<params.length; i++)
       {
         temp = params[i].split("=");
         if ( temp[0] == sname ) { sval = temp[1]; }
       }
  return sval;
}
window.onload = changePic;
var param = getParam("pccsvc");
var serviceName = "images/banner_"+param+".jpg";
function changePic() {
document.getElementById("service").src=serviceName;
}
</script>
</head>
<body>
<img class"resizer" id="service" src="" />
<br>
<br>
<br>

<a href="http://recessiongirlz.info/test-banner.php?pccsvc=revshare" target="_self">revshare</a>
<br>
<a href="http://recessiongirlz.info/test-banner.php?pccsvc=pps" target="_self">pps</a>
<br>
<a href="http://recessiongirlz.info/test-banner.php?pccsvc=if" target="_self">if</a><br>
</body>
</html>