What is Middleware ?

Middleware is a concept where functions can be used to process incoming requests before they reach their final destination and handle outgoing responses before they are sent back to the client.

Express Middleware

An express app can use following types of middleware:-

Application-level middleware Router-level middleware Error-handling middleware Built-in middleware Third-party middleware

Example:-

1. Application level middleware

const express = require('express')
const app = express()

app.use((req, res, next) => {
  console.log('Time:', Date.now())
  next()
})

2. Router-level middleware

const router = express.Router();

router.use((req, res, next) => {
  console.log('Time:', Date.now())
  next()
})

3. Error-handling middleware

app.use((err, req, res, next) => {
  console.error(err.stack)
  res.status(500).send('Something broke!')
})

4. Built-in middleware

express.static

express.json

5. Third-party middleware

cookie-parser
body-parser

const cookieParser = require('cookie-parser')

// load the cookie-parsing middleware
app.use(cookieParser())