ReferenceError：未定义err

Question

I'm started working on my very first API using Mongo, Express and Node. When i tried to make API endponit for one specific user, console throw error ReferenceError: err is not defined . An error appears in the method I already used for auth part, and there it worked fine. The part of code where is the error, on line 5:

exports.userById = (req, res, next, id) => {
   User.findById(id).exec(() => {
       if(err || !user) {
           return res.status(400).json({
               err: "User not found"
           });
       }
       req.profile = user //adds profile object in req with user info
       next();
   });
}

Also, the part of code where I tried to get a single user:

exports.getUser = (req, res) => {
    req.profile.hashed_password = undefined;
    req.profile.salt = undefined;
    return res.json(req.profile); 
}

I don't think the problem could be here, but there is also route line from routes file

router.get("/users/:userId", authController.requireSignin, userController.getUser);

Thanks everyone for the help!

Answer 1

我很确定err来自exec ：

User.findById(id).exec(err => {...});

Answer 2

Edit I guess you want to search by id and return something. Try this.

 User.findById(id, (err, user) => {

    // if error display errort
    if(err) console.error(err);

    // if user do not exists
    if(!user) {// what is user ? the doc result ?
        return res.status(400).json({
            "err": "User not found"   // i think use ""
        });
    }

    req.profile = user //adds profile object in req with user info
    next();

 });