Adding/replacing GET variables in a url

[MadLittleMods]

So I am wanting to replace GET variable values in a url and if the variable does not exist, then add it to the url.

 

I am not good with javascript but I do know how to use jQuery quite well and the basics of javascript. I do know how to write regex but not how to use the javascript syntax of regex and what functions to use it with.

 

Here is what I have so far and it does have an error on line 3: See it on jsfiddle(or below): http://jsfiddle.net/MadLittleMods/C93mD/

function addParameter(url, param, value) {
    var pattern = new RegExp(param + '=(.*?);', 'gi');
    return url.replace(pattern, param + '=' + value + ';');

    alert(url);
}