Express JS Middleware: Everything You Need to Know | Simplilearn

Express is a node js web application framework that provides broad features for building web and mobile applications. It is used to build a single page, multipage, and hybrid web application.

This tutorial on Express Middleware will walk you through all the topics on Express js Middleware.

What Is Middleware?

• A request handler with access to the application’s request-response cycle is known as middleware. 
• It’s a function that holds the request object, the response object, and the middleware function.
• Middleware can also send the response to the server before the request. 
• The next middleware function is commonly represented as a variable named next.
• Simply middleware is a function that can only be applied using routes. 
• We can access and modify request and response data using middleware.

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Functions of Middleware

• Executes any code 
• We can make changes to the request-response objects
• Middleware can also End the request-response cycle
• Middleware can call the next middleware function in a stack 

We use these functions to modify our middleware to perform many tasks. If we want to block our site for some country or if we’re going to check the authentication of a user etc., we use middleware for that.

Creating Middleware 

Now we will create an Express middleware for that we will create a simple Express API. We can create middleware in a router file, but the easiest method is to create a separate middleware file and then execute it; creating and using middleware is very simple.

So to create middleware, we need to install all the packages to run express middleware.

Fig – app.js

• Now open your terminal and run this file we will see our server is running.
• After this, go to the local server and type localhost:4000
• Now we will call our next parameter, 
• In express framework, next is a function

Fig – middleware

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Fig – output 

• Now we will go to the home page that we have created.

Fig – output home page

Conclusion 

This article has touched on what is middleware, the functions of middleware, and we have created a simple middleware using Express js. You can enroll in Simplilearn’s Node JS certification training to learn more about Express. This certification training course will upskill you on how to use Express.js, NPM, NPM Vet, REST, shrink-wrap, Express.js with MongoDB, and SQLite CRUD operations. This Express JS training focuses on the fundamental ideas of Node JS and Express Js and gives you hands-on experience developing an HTTP server.

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