warmup-week11day02-middleware

Middleware and the Middleware Stack

Middleware

Middleware are functions that execute during the lifecycle of a request to the Express server. Each middleware has access to the HTTP request and response for each route it's attached to.

Why middleware?

Middleware allows you to break these request handler functions into smaller bits. These smaller functions tend to handle one thing at a time.

Middleware Stack

Middleware stack is a stack of middleware functions

Types of middleware in express

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

Application-level middleware

Bind application-level middleware to an instance of the app object by using the app.use() and app.METHOD() functions, where METHOD is the HTTP method of the request that the middleware function handles (such as GET, PUT, or POST) in lowercase.

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

Router-level middleware

Router-level middleware works in the same way as application-level middleware, except it is bound to an instance of express.Router(). Load router-level middleware by using the router.use() and router.METHOD() functions.

const router = express.Router()
router.use(function (req, res, next) {
  console.log('Time:', Date.now())
  next()
})

.........etc.