express error handling

express.js

const express = require('express');

const app = express();
// cookie parser
// body parser
// cors
// if applicable

app.use('/api/user', userRoute(express.Router()))

// error handling
app.use((err, req, res, next) => {
  // log error
   if (err instanceof MyError) {
    res.status(err.statusCode).json(err.message);
    
   } else {
      res.status(500).json(err);
   }
  return next();
})


// another file
const asyncHandler = fn => (...args) => {
  const fnReturn = fn(...args);
  const next = args[args.length - 1];
  return Promise.resolve(fnReturn).catch(next);
};

module.exports = (router) => {
  router.route('/:id').get(asyncHandler(getUser))
}

const getUser = async function (req, res) {
  const { id } = req.param;
  if (!id) throw new Error('if has error.');

  const user = await dbCall();

  res.status(200).json({ user });
};

export class MyError extends Error {
  constructor(
    public messages
    public statusCode = 500,
  ) {
    super(message);
}