How to delete Cookie when shutting down the server

So everytime I start my nodejs Server I set the userId:

var customerId = null;  

When the user tries to log in I set the cookie :

customerId = myCart.Login(FormData.username, FormData.password);
_setCookie(res, "customerId=" + customerId);

Set cookie:

function _setCookie(res, cookieStr) {
    res.setHeader('set-cookie', cookieStr);
}

The problem is when I close to application and I restart it the cookie is still setted but the customerId is setted to null. This causes the error when I try to logg off the user:

 if (userIsLogedIn(req, "customerId")) {

            _processFormData(req, res,
                (req, res, FormData) => {

                    myCart.LogOffCustomer(customerId);
                    _delCookie(res, "customerId=" + customerId);
                    myWebServer.redirect(res, "Success.html");

                },

                (res) => {
                    myWebServer.redirect(res, "LoggOffFailed.html");
                }
            );


        }
        else {
            myWebServer.redirect(res, "NotLoggedIn.html");
}

Here I check if the user is logged in:

 function userIsLogedIn(httpMessage, cookieName) {

    if (httpMessage.headers.cookie == undefined) {
        return false;
    }
    var cookies = _parseCookies(httpMessage.headers.cookie);

    return cookies[cookieName] != undefined;
}

function _parseCookies(cookieName) {
    var cookies = {};
    cookieName.split(';').forEach(function (cookie) {
        var parts = cookie.match(/(.*?)=(.*)$/)
        cookies[parts[1].trim()] = (parts[2] || '').trim();
    });

    return cookies;
};

So when I try to logg off the user I check if the cookie is setted. The cookie is only setted when the user is loged in. But when I close the server and restart him the userId is null and so I cant logg off the user.It means that I can only logg off the user if I don't close the server. But I wan't it than even when I reset the server I still can logg off the user.

via igodie