Here is the function
function getQuerystring(key, default_) {
if (default_ == null) default_ = "";
key = key.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
var regex = new RegExp("[\\?&]" + key + "=([^&#]*)");
var qs = regex.exec(window.location.href);
if (qs == null)
return default_;
else
return qs[1];
}
*taken from http://www.bloggingdeveloper.com/post/JavaScript-QueryString-ParseGet-QueryString-with-Client-Side-JavaScript.aspx