Using jQuery to modify QueryString

I recenlty worked on a requirement where I have to modify the querystring of all the links in a page before the actual request is made from the browser, i.e. when a link is clicked. There may be better ways to do this but this is how I implemented it using jQuery.

$(document).ready(function() {
    $('a').click(function(event) {

        var $a = $(event.target);

        if ($a.is('a')) { //if the event is triggered by an <a> tag

           //append refid querystring to href
if it is not an external url and it refers to 
an ASPX page and does not already contain 
refid in querystring 

            var appendrefid = 
$a.attr("href").toLowerCase().indexOf("http://") == -1 
            &&
$a.attr("href").toLowerCase().indexOf("https://") == -1 
            &&
$a.attr("href").toLowerCase().indexOf(".aspx") != -1 
              && 
$a.attr("href").toLowerCase().indexOf("refid=") == -1;

            if (appendrefid) {

                event.preventDefault();
                location.href = $a.attr("href") + "?refid=" + GetQStringVal("refid");
            }
        }
    });
});

/* function to read value of the given key, x, from querystring */
function GetQStringVal(x) {

    var a = location.search.substring(1); var b = a.split("&");

    for (var i = 0; i < b.length; i++) {
        var c = b[i].split("=");
        if (c[0].toLowerCase() == x.toLowerCase()) { return c[1]; }
    }

    return "";
}

Here the main page, where the content is coming from the database, is always requested with refid in the querystring and the above script reads the refid from the original request and appends it to the newly requested page when the link is clicked.