What are Node.js middleware and how do I use them?

What are Node.js middleware and how do I use them?

Node.js middleware are functions that have access to the request and response objects in an application. They can modify the request, end the response, or call the next middleware function. You can use them for tasks like logging, authentication, and error handling.

Can you give me an example of a simple middleware function?

Sure! Here's a simple logging middleware:

function logger(req, res, next) {
    console.log(`${req.method} ${req.url}`);
    next(); // Call the next middleware
}

You can use this in your Express app by adding app.use(logger);.

How do I handle errors with middleware?

You can create an error-handling middleware by defining a function with four parameters: err, req, res, and next. Here's an example:

function errorHandler(err, req, res, next) {
    console.error(err);
    res.status(500).send('Something went wrong!');
}

Add it after all other middleware.

What are some common use cases for middleware?

Common use cases include logging requests, handling authentication, parsing request bodies, and managing sessions.