What is middleware in NodeJS and its uses

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What is middleware in NodeJS and its uses





Middleware is a software that sits between an operating system and application, providing services and resources to the application. In Node.js, middleware refers to functions that have access to the request and response objects, and the next function in the request-response cycle. These functions are used to perform tasks such as logging, authentication, and validation.

Node.js has a built-in middleware system called Express.js, which is a popular framework for building web applications. Express.js allows developers to easily define and use middleware functions in their application.

To use middleware in an Express.js application, you first need to import the Express module and create an instance of the Express application. Then, you can use the app.use() method to define and add middleware functions to the application. These functions will be executed in the order they are defined, before the final route handling function.

For example, to create a middleware function that logs the date and time of each request, you can use the following code:

app.use(function(req, res, next) {
    console.log("Time: ", Date.now());
    next();
});

This middleware function logs the current time, and then calls the next() function to move on to the next middleware function or route handling function in the request-response cycle.

Middleware functions can also be used to handle errors in an application. For example, you can create a middleware function that is specifically responsible for handling errors and sending the appropriate response to the client.

app.use(function(err, req, res, next) {
    console.error(err.stack);
    res.status(500).send('Something broke!');
});

In addition to built-in middleware functions, developers can also create their own custom middleware functions. These functions can be defined in a separate module and imported into the application, making it easy to reuse the same functionality across multiple routes.

Middleware functions are an important aspect of building web applications with Node.js and Express.js. They provide a way to easily perform tasks such as logging, authentication, and validation, as well as handle errors and improve the overall structure of the application.

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