Middleware in Express.js
Middleware in Express.js – Complete Beginner Guide
Middleware in Express.js is a core concept used in backend development. It allows you to process requests before sending a response. Middleware functions are used for tasks like authentication, logging, validation, and error handling.
What is Middleware in Express.js
Middleware in Express.js is a function that runs between the request and the response. It has access to the request object, response object, and the next function.
Syntax of Middleware
// logic here
next();
}
The next() function is very important. It passes control to the next middleware or route handler.
Types of Middleware in Express.js
Application-level middleware is used for all routes.
Router-level middleware is used for specific routes.
Built-in middleware is provided by Express like express.json().
Third-party middleware is installed using npm.
Application-Level Middleware Example
const app = express();
app.use((req, res, next) => {
console.log(“Request received”);
next();
});
app.get(‘/’, (req, res) => {
res.send(“Home Page”);
});
app.listen(3000);
Route-Level Middleware Example
console.log(“Auth checked”);
next();
};
app.get(‘/dashboard’, checkAuth, (req, res) => {
res.send(“Dashboard”);
});
Built-in Middleware Example
This middleware is used to parse JSON data from request body.
Third-Party Middleware Example
app.use(morgan(‘dev’));
Morgan is used for logging HTTP requests.
Why Middleware is Important
Middleware in Express.js helps in handling common tasks. It keeps code clean and reusable. It also improves application structure.
Real-World Use Cases
Authentication and authorization
Logging requests
Handling errors
Parsing request data
Best Practices
Keep middleware simple and focused. Always call next() when needed. Use separate files for middleware. Avoid blocking code.
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FAQs
What is middleware in Express.js
Middleware is a function that runs between request and response.
What is next() in middleware
It passes control to the next middleware.
Can we use multiple middleware
Yes, multiple middleware can be used in sequence.
Why is middleware important
It helps in code reuse and better structure.