Middleware in Express

Middleware Chaining

Different middlewares in the express can be chained together, so whenever a request is sent to the server, it goes through a series of middleware, and the middleware are executed in the order in which they are chained. The last function sends the response back to the server.

To achieve the chaining in express next() function is used, which is responsible for calling the next middleware function.

In the above diagram, we can see that a request is being sent through different middleware and operations are being performed and the last middleware sends the response back to the server.

Now we know about middleware and middleware chaining, lets try to implement a simple middleware in the express.

Implementing Middleware

Before we start implementing middleware, make sure that you have Node.js installed on your PC. If you have Node.js installed, then create a new node project and install express as a dependency using the following command.

Once the express is installed the create an app.js file in the directory. Now open the app.js file in any code editor of your choice and write down this code.

Output

Every time the app receives a request, “Visited home page “ is logged into the console.

Advantages of Middleware

Below are some of the advantages of using the middleware in express

1. Middleware can be used to implement the login and authentication
2. Middleware improves the client-side rendering.
3. Middleware helps in optimization and better performance
4. Middleware can be used for error handling.

Frequently Asked Question

1. What is Middleware in Expree.js?
   Middleware functions have access to the request object (req), the response object (res), and the next function in the application’s request-response cycle. The next function is a function in the Express router that, when invoked, executes the middleware succeeding the current middleware.
2. What is middleware chaining?
   Different middlewares in the express can be chained together, so whenever a request is sent to the server it goes through a series of middleware and the middleware are executed in the order in which they are chained. The last function sends the response back to the server.

Key Takeaways

This article discussed middleware in js in detail, along with its syntax, use, and implementation. We also discussed the middleware chaining in detail.

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