How do you handle errors in Express.js?

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In Express.js, errors are handled using middleware specifically designed for error handling. Here’s how it works:

1. Error-Handling Middleware:
   Express identifies a function as an error handler if it has four parameters: (err, req, res, next). This function catches errors thrown in route handlers or other middleware and allows you to send a proper response to the client.

2. Throwing or Passing Errors:

   • You can throw errors inside a route or middleware using throw new Error("message").

   • Alternatively, you can pass an error to the next middleware using next(error). Express will skip all normal middleware and route handlers and move directly to the error-handling middleware.

3. Custom Error Response:
   Inside the error-handling middleware, you can log the error, set HTTP status codes (like 400, 404, 500), and send a JSON or HTML response with the error message. This ensures clients get a structured and informative response instead of a server crash.

4. Catch-All for Unhandled Routes:
   It’s a good practice to define a middleware that catches 404 errors for routes that don’t exist. Then, you can forward these to the error-handling middleware.

Summary:
Errors in Express.js are managed using a combination of try-catch, next(error), and dedicated error-handling middleware. This ensures your application can gracefully handle unexpected issues and provide meaningful feedback to the client.

Read More :

What is the difference between app.use() and app.get() in Express?

What is Express.js, and why is it used in Node.js applications?

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