Why cant I inline call to res.json?

Question

I have and expressjs application and on a specific route I call a function that responds with a user from the database by calling res.json with the database doc

Answer 1

The json function loses its correct this binding when used like that since .then is going to invoke it directly without reference to the res parent object, so bind it:

var getUserInline = function(req, res) {
    getUserFromDatabase().then(res.json.bind(res));    
}