Express Middleware: What and how to create middleware

Node.js / June 15, 2020 / TopCode / 0

Introduction:

The Express middleware is a powerful tool for creating web applications in Node.js. It allows developers to quickly and easily add functionality to their applications by using a variety of pre-built functions. In this blog post, we will explore Express middleware and look at how to create custom middleware functions.

Middleware is a function in Express that acts as a bridge between the server and the client. It offers the opportunity to modify each request that comes into the server. For example, it can do anything from logging information about each request, to checking for authentication, to modifying data before being sent to the client. Express middleware is typically used to add functionality to a web application. Express comes with a number of built-in middleware functions such as serving static files, logging requests, and parsing requests. It also allows for custom middleware that can be used to meet the specific needs of an application. Middleware is an important part of the Express framework and can be used to make web applications more powerful and efficient

Express Middleware with Code Example

Middleware is invoked between the request and the response of an application. It provides a way to perform tasks such as authentication, data validation, error logging, and more. Middleware functions take three arguments: request, response, and next. Here is an example of an Express middleware function that logs a message in the console whenever a request is received:

const loggerMiddleware = (request, response, next) => {
console.log(`Received a ${request.method} request at ${request.url}`);
next();
};

In the above example, the loggerMiddleware function takes the arguments of request, response, and next, and prints out the method and URL of the request. After logging the request, the function must call the next() function to allow the request to continue processing.

The Express framework provides a large number of built-in middleware functions, such as body-parsing, cookie-parsing, and session-storing. These functions can be easily enabled in an application by using the app.use() method. Here is an example of how to set up body-parsing middleware in Express:

app.use(express.json());
app.use(express.urlencoded({ extended: true }));

How to Create Custom Middleware

In addition to the built-in middleware, developers can create their own custom middleware functions. Custom middleware can be used to perform tasks such as authentication, logging, data validation, and more. To create custom middleware, the developer must create a function with the same three arguments as the built-in middleware functions: request, response, and next. Here is an example of a custom middleware function that logs the IP address of the request:

const ipLoggerMiddleware = (request, response, next) => {
console.log(`IP address of request is ${request.ip}`);
next();
};

Custom middleware can then be enabled using the app.use() method. The following example shows how to enable the ipLoggerMiddleware:

app.use(ipLoggerMiddleware);

By using custom middleware, developers can easily add custom functionality to their applications.

Conclusion

Middleware is a powerful tool for creating web applications and adding custom functionality. It allows developers to quickly and easily add pre-built functions to their applications, as well as create their own custom middleware functions. In this blog post, we have explored middleware and looked at how to create custom middleware functions.

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