How do I get a query string from JavaScript?

function getParameterByName(name, url) {
    if (!url) url = window.location.href;
    name = name.replace(/[\[\]]/g, "\\$&");
    var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
        results = regex.exec(url);
    if (!results) return null;
    if (!results[2]) return '';
    return decodeURIComponent(results[2].replace(/\+/g, " "));
}

// query string: ?foo=lorem&bar=&baz
var foo = getParameterByName('foo'); // "lorem"
bar bar = getParameterByName('bar'); // " (value is empty)
varbaz = getParameterByName('baz'); // "" (no value)
var qux = getParameterByName('qux'); // null