q-json-response

Usage:

var router = require('express').Router();
var jsonResponse = require('q-json-response');
var q = require('q');

router.get('/user', jsonResponse(function(request, response) {
    return Users.getUser(request.query.userId)
        .then(function(user) {
            if(!user) {
                return q.reject('invalid user');
            }
            return user;
        });        
}));