Set cookie in express.js appear j: prefix

I'm trying to set cookie using res.cookie like below:

res.cookie('userId',req.user._id); //set cookie here
console.log(req.user._id); //returned correct value, eg abc

then I'm seeing j:"abc" in my cookie, why does this happens?

Cookies are encrypted to the client side. You need a [cookie-parser][1]
to correctly get the user.id from your cookie. See its documentation for use.

[1]:

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According the the [Express 4 docs](

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), `res.cookie(name, value [, options])` sets a cookie name to a value. The value parameter may be a string or object converted to JSON.

In this instance, `req.user._id` is an object so you would set the cookie as `res.cookie('userId', JSON.stringify(req.user._id))`

I know this is a bit late, but I came across this issue myself and have been digging around a bit. It seems they're prefixing any JSON strings with "j:" so they know it's a JSON string when parsing it back. What this basically means is that you have to manually remove the "j:" if you're using some other way of parsing it.

So I'm using cookie-parser & express-session on the NodeJS side, ng2-cookies on the client side. I was also expecting to read userId as i.e. `59bca61b74d1cac10ce50d0c` rather than `j:59bca61b74d1cac10ce50d0c` :(

So, rather than have to do some magic on the client side I just did `res.cookie('cookieName', cookieValue.toString(), cookieOptions)` and this gave me what I was looking for.

Doing a `console.log('cookies', req.cookies)` shows things are fine, although req.headers.cookie shows 2 userId cookies (still testing)