JS: get querystring param by name

function getQueryStringParam(name) {
    var ret = null;
    var rxStr = "[&?]" + name + "=([^&?]*)";
    var rx = new RegExp(rxStr);
    if (rx.test(window.location.search)) {
        ret = (window.location.search.match(rx))[1];
        ret = decodeURIComponent(ret.replace(/\+/g, '%20'));
    }
}