get query string param values by key name, optional url - uses location if none

getParameterByName.js

function getParameterByName(name, url) {
    var a = document.createElement('a');
    a.href = url || location.href;
    name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
        results = regex.exec(a.search);
    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}