Error Handling in Express

When building an Express.js application, it's crucial to implement error handling to handle any unexpected errors that may occur during the request-response cycle. Error handling ensures that your application remains stable and provides meaningful feedback to users when errors occur.

Handling Errors with Middleware

In Express, you can handle errors by creating middleware functions that have an additional err parameter. If an error occurs in a previous middleware function or route handler, you can pass the error to the next middleware function by calling next(err). This allows you to consolidate error handling logic in a centralized place.

Here's an example middleware function that handles errors:

1// Example middleware to handle errors
2app.use((err, req, res, next) => {
3  console.error(err);
4  res.status(500).json({
5    message: 'Internal Server Error',
6  });
7});

This middleware function logs the error to the console and sends a JSON response with a 500 status code and a message indicating an internal server error.

Error Handling for Asynchronous Code

When working with asynchronous code in Express, it's important to handle errors that occur in promises or async/await functions. You can do this by using a try/catch block inside the asynchronous code and calling next(err) with the error as an argument.

Here's an example of error handling in an async/await function:

1app.get('/users', async (req, res, next) => {
2  try {
3    const users = await getUsers();
4    res.json(users);
5  } catch (err) {
6    next(err);
7  }
8});

In this example, if an error occurs in the getUsers function, it will be caught in the catch block and passed to the next middleware function for error handling.

Error handling in Express is an essential part of building robust and reliable applications. By implementing error handling middleware and handling errors in asynchronous code, you can handle and respond to errors effectively.

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// Example middleware to handle errors

app.use((err, req, res, next) => {

  console.error(err);

  res.status(500).json({

    message: 'Internal Server Error',

  });

});