<!DOCTYPE html>
Express.js Middleware: Step-by-Step Walkthrough
Middleware functions in Express.js provide a way to perform tasks before the request is passed to the route handler. It can be used for logging, security checks, authentication, and more. In this tutorial, we will go through a step-by-step walkthrough of how middleware works in Express.js.
What is Middleware in Express.js?
Middleware functions in Express.js are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. These functions can perform tasks such as logging, authentication, authorization, parsing request bodies, and more.
Creating Middleware in Express.js
To create a middleware function in Express.js, you simply write a function that takes three parameters: req, res, and next. Here’s an example of a simple middleware function that logs the request method and URL:
function logRequest(req, res, next) {
console.log(`${req.method} ${req.url}`);
next();
}
In this example, the logRequest middleware function logs the request method and URL to the console and then calls the next middleware function with the next() function.
Using Middleware in Express.js
Once you have created a middleware function, you can use it in your Express.js application by passing it as an argument to the app.use() method. For example:
app.use(logRequest);
This will apply the logRequest middleware function to all incoming requests to your Express.js application.
Order of Middleware Execution
Middleware functions in Express.js are executed in the order in which they are defined. It is important to pay attention to the order of your middleware functions to ensure that they are executed in the correct sequence. You can use the next() function to pass control to the next middleware function in the chain.
Conclusion
Middleware functions in Express.js are a powerful feature that provides a flexible way to handle tasks before passing the request to the route handler. In this tutorial, we learned how to create and use middleware functions in Express.js. By understanding how middleware works, you can create robust and secure web applications using Express.js.
Awesome ❤❤❤