Middleware
Definition
Functions that have access to the request object, response object, and the next middleware function in the application’s request-response cycle. They execute in the middle of the flow.
Explain Like I'm New
Middleware is the assembly line. A raw request enters the factory. Station 1 (Middleware) checks if it's JSON. Station 2 logs the time. Station 3 checks if the user is an Admin. If all stations approve, the request finally reaches the end of the line (your Route) where the database is updated. If a station rejects it, the line stops instantly.
Real World Example
Protecting a route. You write an `isAuthenticated` middleware function. You plug it into your `/dashboard` route. If the user isn't logged in, the middleware immediately returns a 401 Error. If they are, it calls `next()` to let them through to the dashboard.
Common Use Cases
- •Authentication/Authorization
- •Logging
- •Parsing JSON payloads
- •CORS configuration
Interactive Example
Interview Questions
basic
- What crucial function must a middleware call to allow the request to continue?
intermediate
- What happens if a middleware doesn't call `res.send()` and doesn't call `next()`?