Express.js Error Handling

In Express.js, error handling can be done using middleware functions. When an error occurs in your application, Express.js will pass the error object to the next error-handling middleware function. Here’s an example of how you can implement error handling in Express.js.

error-handling middleware

Let’s create an error-handling middleware function.

app.use((err, req, res, next) => {
  // Default status code to 500 if it's not set
  const statusCode = res.statusCode !== 200 ? res.statusCode : 500;

  // Set the status code and send the error message
  res.status(statusCode).json({
    message: err.message,
    stack: process.env.NODE_ENV === 'production' ? '' : err.stack
  });
});

How to use the error-handling middleware function

Use the error-handling middleware function in your application

// Define your routes and middleware functions
app.get('/', (req, res, next) => {
  // Example error, assuming `someFunction` throws an error
  try {
    someFunction();
  } catch (err) {
    next(err); // Pass the error to the error-handling middleware
  }
});

// Start the server
app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

In this example, when an error occurs in the route handler (/), the next(err) statement is called to pass the error object to the error-handling middleware. The middleware function then sets the appropriate status code and sends a JSON response with the error message.

It’s important to define the error-handling middleware after all other routes and middleware functions in your application, as Express.js will sequentially pass the error to the next error-handling middleware function if one exists.

Remember to replace someFunction() with your actual code that might throw an error. You can customize the error-handling middleware to suit your needs, such as logging the error or providing additional error details based on your application’s requirements.

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