Adding a parameter to the URL with JavaScript

Question

In a web application that makes use of AJAX calls, I need to submit a request but add a parameter to the end of the URL, for example:

Original URL:

Answer 1

If you're messing around with urls in links or somewhere else, you may have to take the hash into account as well. Here's a fairly simple to understand solution. Probably not the FASTEST since it uses a regex... but in 99.999% of cases, the difference really doesn't matter!

function addQueryParam( url, key, val ){
    var parts = url.match(/([^?#]+)(\?[^#]*)?(\#.*)?/);
    var url = parts[1];
    var qs = parts[2] || '';
    var hash = parts[3] || '';

    if ( !qs ) {
        return url + '?' + key + '=' + encodeURIComponent( val ) + hash;
    } else {
        var qs_parts = qs.substr(1).split("&");
        var i;
        for (i=0;i