nodejs Appending date object to user in session

I have set up nodejs with express, sessions, mongoose etc. Login and navigation works all fine, now I just want to append additional information to the user, specifically a date object.

Here is how I attempted to do that:

var user = req.body.user;
if(user) {
    if(!user.viewdate)
        user.viewdate = new Date();
}

Note - I removed a lot of my code to highlight the problem at hand.

Now for some reason when I do that, Nodejs tells me that user.viewdate is actually a string and not a Date object, which means that I can't access any of the date functions.

console.log(typeof(user.viewdate) + ", " + user.viewdate);
// prints: string, 2017-05-23T13:37:57.672Z

user.viewdate.getDate();
// TypeError: user.viewdate.getDate is not a function

I have actually solved the problem by converting the string to a date object, editing it, and then converting it to a string again.

var date = new Date(user.viewdate);
date.setDate(date.getDate() + 1);
user.viewdate = date;

But all this converting seems tedious and unnecessary when I could just access the actual date.

Can someone tell me, if it's possible to save a Date attribute to a user in a session?

via Felix Jassler