function changeURLPar(url, ref, value) {
    var str = "";
    if (url.indexOf('?') != -1)
        str = url.substr(url.indexOf('?') + 1);
    else
        return url + "?" + ref + "=" + value;
    var returnurl = "";
    var setparam = "";
    var arr;
    var modify = "0";
    if (str.indexOf('&') != -1) {
        arr = str.split('&');
        for (i in arr) {
            if (arr[i].split('=')[0] == ref) {
                setparam = value;
                modify = "1";
            }
            else {
                setparam = arr[i].split('=')[1];
            }
            returnurl = returnurl + arr[i].split('=')[0] + "=" + setparam + "&";
        }
        returnurl = returnurl.substr(0, returnurl.length - 1);
        if (modify == "0")
            if (returnurl == str)
                returnurl = returnurl + "&" + ref + "=" + value;
    }
    else {
        if (str.indexOf('=') != -1) {
            arr = str.split('=');
            if (arr[0] == ref) {
                setparam = value;
                modify = "1";
            }
            else {
                setparam = arr[1];
            }
            returnurl = arr[0] + "=" + setparam;
            if (modify == "0")
                if (returnurl == str)
                    returnurl = returnurl + "&" + ref + "=" + value;
        }
        else
            returnurl = ref + "=" + value;
    }
    return url.substr(0, url.indexOf('?')) + "?" + returnurl;
}