Execute a middleware function before running the route handler; for example, run it before the findAll method in SongsController. In contrast to frameworks like Express, Nest.js middleware offers a more organized and modular approach, closely aligning with object-oriented programming and functional programming paradigms.

The middleware will have access to req, res, and the next function, allowing customization of the request object. This is similar to Express, but Nest.js provides a more robust and scalable architecture for building complex applications.

Send the request to the server via a browser. In the Nest.js application, execute the logger middleware prior to running the request handler. This architecture follows Nest.js's modular approach, wherein middleware like logging functions can be organized and re-used across different modules more effectively than in a framework like Express, which lacks such a built-in modular system.

Logger systems are essential for tracking activity, diagnosing issues, and understanding the behavior of an application. Unlike traditional setups where logging might be an afterthought, Nest.js allows the integration of sophisticated logging mechanisms due to its modular and extensible nature. This is in contrast to less opinionated frameworks like Express, where logging is often implemented via external middleware without any standard structure.

---
title: Middleware in Nest.js
privateVideoUrl: https://fullstack.wistia.com/medias/5dgnli838e
isPublicLesson: true
---

## What is Middleware in Nest.js

![What is Middleware in Nest.js](https://d2uusema5elisf.cloudfront.net/courses/nestjs-fundamentals/module_03/lesson_03.01/public/assets/what-is-middleware.png)

Execute a middleware function before running the route handler; for example, run it before the findAll method in SongsController. In contrast to frameworks like Express, Nest.js middleware offers a more organized and modular approach, closely aligning with object-oriented programming and functional programming paradigms.

The middleware will have access to req, res, and the next function, allowing customization of the request object. This is similar to Express, but Nest.js provides a more robust and scalable architecture for building complex applications.

![What can Middleware do](https://d2uusema5elisf.cloudfront.net/courses/nestjs-fundamentals/module_03/lesson_03.01/public/assets/what-middleware-can-do.png)

-   Execute any code within middleware.
    In Nest.js, middlewares are similar to their Express.js counterparts but are more class-based and modular, fitting well within Nest's strong modular architecture. Unlike in Express, where middleware can sometimes become unmanageable in large applications, Nest.js provides a more structured way to handle middleware.
-   Modify the request (`req`) object.
    In traditional Express.js, this is often done directly within the middleware function. In Nest.js, however, you can lean more on Dependency Injection (DI) and modularity to make these changes in a more organized fashion.
-   End the response cycle.
    Just like in Express, middleware in Nest.js can terminate the request-response cycle. However, Nest.js middleware leverages async/await and decorators, offering a more modern approach and cleaner syntax for handling such operations.
-   Call the next middleware in the stack.
    Both in Nest.js and Express, middleware can pass control to the next middleware function in the stack using the `next()` function. However, Nest.js brings type safety and DI into the picture, making it easier to build robust and maintainable applications.

Haider Malik

Middleware in Nest.js

A middleware function runs before executing the route handler.

Inside the controller, songs controller, I have the find all route handler and

If you want to run any function before executing the route handler, you can

This is a function a browser wants to fetch the songs.

Before fetching the songs, would you like to call any method?

Would you like to execute any type of code?

Middleware can have request object, response, object and next function.

It means you can customize the request object.

If you want to add header, if you want to log the request time, you can do that

A middleware can execute any type of code.

If you want to add the request header, authentication token to the request, you

You can end the request and response cycle.

You can call the next middleware function by calling the next method.

We're going to build the logarind middleware.

Let's imagine you want to send request from your browser to server.

Before executing the route handler, I would like to log the request message for

We're going to build a class-based middleware.

And to create a middleware, you need to implement the next middleware interface

It provides the use method and use method will have the request, response and

Here I'm just logging the request date time.

And at the end, I'm also calling the next function.

If you will not call the next function, it will not go to the next step.

One more thing, middleware is like a dependency.

Here we are injecting the middleware as a dependency.

To inject the middleware as a dependency, we need to implement the next module

It will provide the configure method and the consumer will be middleware

And we just need to call the apply method from the consumer object.

And you need to provide the logger middleware.

Here you need to specify where do you want to implement the logger middleware.

Before creating a middleware, I'm going to use Nest CLI.

Please give me the help for Nest generate command.

You can see that I got all the commands related to Nest generate.

You can generate class controller decorator filter guard middleware by provider

Please do not create directory for no spec.

I'm going to place all my middlewares inside the command directory.

Nest generate my command slash middleware and the name of the middleware which

Let's try with no flat and dash dash dry run.

It will not create the actual file but got the steps.

You will get the understanding how it will run.

But when you execute this code, it will create the logger middleware file

You can see that it has already implemented the nest middleware interface.

And I got the use method with these three arguments request response in the

Here you can customize the request object.

If you want to add your custom logic, you can do it here.

You can do it whatever you want to do dot to that string.

Now I told you what I taught you how to apply the middleware.

You can see that I got the configure method.

And we need to call consumer dot apply the name of our middleware, which is

If you will send the request to the root URL, which is localhost colon 3000,

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