were do you get the req and res in express js code example

Example 1: express hello world

//to run : node filename.js
const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`Example app listening at http://localhost:${port}`))

//visit localhost:3000
// assuming you have done 1) npm init 2) npm install express

Example 2: express router middleware

var express = require('express')
var app = express()
var router = express.Router()

// a middleware function with no mount path. This code is executed for every request to the router
router.use(function (req, res, next) {
  console.log('Time:', Date.now())
  next()
})

// a middleware sub-stack shows request info for any type of HTTP request to the /user/:id path
router.use('/user/:id', function (req, res, next) {
  console.log('Request URL:', req.originalUrl)
  next()
}, function (req, res, next) {
  console.log('Request Type:', req.method)
  next()
})

// a middleware sub-stack that handles GET requests to the /user/:id path
router.get('/user/:id', function (req, res, next) {
  // if the user ID is 0, skip to the next router
  if (req.params.id === '0') next('route')
  // otherwise pass control to the next middleware function in this stack
  else next()
}, function (req, res, next) {
  // render a regular page
  res.render('regular')
})

// handler for the /user/:id path, which renders a special page
router.get('/user/:id', function (req, res, next) {
  console.log(req.params.id)
  res.render('special')
})

// mount the router on the app
app.use('/', router)