get querystring params

qs.js

function gup(name, url, defaultValue) {
    if (!url) url = location.href;
    name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
    var regexS = "[\\?&]" + name + "=([^&#]*)";
    var regex = new RegExp(regexS);
    var results = regex.exec(url);
    return (results == null ? null : results[1]) || defaultValue;
}

var id = gup('id', document.location.toString(), '50');