MERN stack err.kind expression: Where does it come from?

I’m trying to go into MERN stack development lately, and I saw in a tutorial an Error Handling expression being used in order identify what type of error is being thrown. As I’ve seen so far, below expressions can be used, and they seem to be using standard js libraries.

err.name === "example"
err.message.indexOf('Cast to ObjectId failed') !== -1
err.message instanceof mongoose.Error.CastError

But then I saw this way of handling an error, which is using the "error.kind" property. I went around to figure out where it comes from and what kind of values I should be expecting from it without success.

Hoping you can shed some light on below questions:

  • From which library is "error.kind" coming from ? is it coming from the standard JS code library ?
  • Is it coming from Mongoose ? Node ? Express ?

I’m obviously still confused at this stage, so happy to go over any reading material you’d recommend.

router.get('/user/:user_id',async (req,res)=>{

    try {
        const profile = await Profile.findOne({user:req.params.user_id}).populate('User',['name','avatar']);
        


    if(!profile){
        return res.status(400).json({msg:'There is no profile for the user'});
    }

    res.json(profile);

    } catch (err) {

        console.log(err.message);
        
        if(err.kind == 'ObjectId'){
            return res.status(400).json({msg:'There is no profile for the user'});
        }

        res.status(500).json({msg:'Server Error'});
    }

});

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