specific-errors-handling.js

if (err instanceof AuthenticationError) {
    return res.status(401).send('not authenticated');
}

if (err instanceof UnauthorizedError) {
    return res.status(403).send('forbidden');
}

if (err instanceof InvalidInputError) {
    return res.status(400).send('bad request');   
}

if (err instanceof DuplicateKeyError) {
    return res.status(409).send('conflict. entity already exists');
}

// Generic error
return res.status(500).send('internal error occurred')