Express error handling

server.js

class BadError extends Error {
  get type() { 'very bad' }
}

require('express')()
  // Express will convert this synchronous throw
  .get('/', (_req, res) => {
    throw new BadError('threw an error: failed')
  })
  // Into a pipeline error, handled here:
  .use((err, _req, res, _next) =>
    res.send(`[${err.constructor.name}] ${err.message}`))
  .listen(9998)