express-next-falsy.js

'use strict'

const express = require('express')
const axios = require('axios')
const format = require('util').format

const app = express()

app.use(function (request, response, next) {
  console.log('Got request')

  // any of these

  // throw undefined
  // next()
  // next(undefined)

  // throw null
  // throw ''
  // throw false
  // throw 0
  // next(null)
  // next('')
  // next(false)
  // next(0)
})

app.use(function (error, request, response, next) {
  console.log('I want to handle the error but get never called.')

  console.trace(error)

  response.json("Don't Panic!")
})

app.listen(3001, function () {
  console.log('Listening ...')

  axios('http://localhost:3001')
    .then(function (response) {
      console.log(`Got response ${format(response)}`)
    })
    .catch(function (error) {
      console.trace(`Uh Oh: ${format(error)}`)
    })
})