notes.js

// routes/notes.js
...
exports.updateNote = function(req, res) {
    var id = req.params.id;
    Note.findById(id, function (err, doc){        
        if(!err) {
            doc.title = req.body.title;
            doc.note = req.body.note;
            doc.save(function(err, result) {
                if (err){
                    res.send({'error':'An error has occurred'});
                }
                else {
                    res.send(result);
                }
            });
        }
        else{
            var note = new Note();
            note.title = req.body.title;
            note.note = req.body.note;
            note.save(function (err, doc) {
                if (err) {
                    res.send({'error':'An error has occurred'});
                }
                else{
                    res.send(doc);
                }
            });    
        }    
    }); 
}
...