Middleware in Node js is a function that plays a vital role in the request-response lifecycle of Node js execution. In the context of web development, middleware is a term used to describe software elements that reside between multiple application components and manage activities including request processing, authentication, logging, and error handling. Middleware connects the client’s request and the server’s response, to put it another way.

Before handing off control to the following middleware in the chain, middleware functions can conduct operations on or alter the request and response objects since they have access to them and are successively operated. This sequential execution enables programmers to separate an application’s complex logic into manageable chunks.

Middleware in Node Js

The Node.js web frameworks Express.js, Koa.js, and Hapi.js regularly use middleware. These frameworks provide a dependable way to manage middleware and incorporate it into the application’s architecture.

A function that has access to request objects, response objects, and subsequent middleware functions is all that middleware is. It is present between the Node.JS execution cycles for requests and responses. The variable ‘req’ usually refers to the request object, whereas the variable ‘res’ usually refers to the response object. It should be noted that middleware can handle ‘req’ objects before the server sends a response.

There are many things we can do with Node.JS middleware. With middleware functions, we can run any code at first. Additionally, we can modify the response and request objects. The request and response cycle can be stopped during Node.JS operation. The following middleware function in the queue for Node.JS execution can also be called.

Middleware Stack

Middleware operations are arranged in a stack in Express.js, and they are carried out in the order they are added to the stack. You can adequately manage the flow of requests and responses due to this sequential execution. Middleware can be installed locally, which only affects particular routes or route groups, or globally, which affects all routes.