How to add parameters to a URL that already contains other parameters and maybe an anchor

Question

I'm wondering how I can add a new parameter to an existing url. The problem is: the url may also contain an anchor.

For example:

http://www.example.com?foo=bar#hashme

And I want to add another parameter to it, so it results in this:

http://www.example.com?foo=bar&x=y#hashme

Answer 1

I used parts of The Awesome One's solution, and a solution found on this question:

Adding a parameter to the URL with JavaScript

Combining them into this script:

function addParameter(url, parameterName, parameterValue, atStart/*Add param before others*/){
    replaceDuplicates = true;
    if(url.indexOf('#') > 0){
        var cl = url.indexOf('#');
        urlhash = url.substring(url.indexOf('#'),url.length);
    } else {
        urlhash = '';
        cl = url.length;
    }
    sourceUrl = url.substring(0,cl);

    var urlParts = sourceUrl.split("?");
    var newQueryString = "";

    if (urlParts.length > 1)
    {
        var parameters = urlParts[1].split("&");
        for (var i=0; (i < parameters.length); i++)
        {
            var parameterParts = parameters[i].split("=");
            if (!(replaceDuplicates && parameterParts[0] == parameterName))
            {
                if (newQueryString == "")
                    newQueryString = "?";
                else
                    newQueryString += "&";
                newQueryString += parameterParts[0] + "=" + (parameterParts[1]?parameterParts[1]:'');
            }
        }
    }
    if (newQueryString == "")
        newQueryString = "?";

    if(atStart){
        newQueryString = '?'+ parameterName + "=" + parameterValue + (newQueryString.length>1?'&'+newQueryString.substring(1):'');
    } else {
        if (newQueryString !== "" && newQueryString != '?')
            newQueryString += "&";
        newQueryString += parameterName + "=" + (parameterValue?parameterValue:'');
    }
    return urlParts[0] + newQueryString + urlhash;
};

Example: addParameter('http://www.example.com?foo=bar#hashme', 'bla', 'valuebla', false)

Results in http://www.example.com?foo=bar&bla=valuebla#hashme