10 NestJS Exception Handling Best Practices

NestJS is a popular Node.js framework for building efficient, reliable, and scalable server-side applications. It is based on Express and written in TypeScript. Exception handling is an important part of any application, and NestJS provides a robust system for handling errors and exceptions.

In this article, we will discuss 10 best practices for exception handling in NestJS applications. We will look at how to properly handle errors and exceptions, as well as how to log them for debugging purposes. We will also discuss how to use the built-in exception filters to make your code more robust.

1. Use the @Catch decorator

The @Catch decorator allows you to easily define a custom exception handler for any given route or controller. This makes it easy to handle errors in an organized and consistent way, without having to manually write try/catch blocks everywhere.

The @Catch decorator also provides the ability to customize error messages based on the type of error that was thrown. For example, if a user tries to access a resource they don’t have permission to view, you can return a customized message informing them of this.

Overall, using the @Catch decorator is a great way to ensure your NestJS application handles exceptions in a clean and efficient manner.

2. Create a custom exception filter

A custom exception filter allows you to easily catch and handle errors in a consistent way. This means that instead of having to manually check for errors in each controller, you can create a single filter that will be applied across all controllers. This makes it easier to debug issues and maintain your codebase.

Additionally, creating a custom exception filter gives you more control over how errors are handled. You can decide which types of errors should be logged, which ones should be sent to an external service like Sentry, and which ones should be displayed to the user. This helps ensure that users get the best experience possible when using your application.

3. Create an error handler class

When you create an error handler class, it allows you to centralize all of your exception handling logic in one place. This makes it easier to maintain and debug any errors that may occur. It also helps keep your codebase organized and readable.

The error handler class should contain methods for each type of exception you want to handle. For example, if you’re dealing with a database connection issue, you could have a method called “handleDatabaseError()” which would be responsible for logging the error and returning a response to the user.

By creating an error handler class, you can easily add new types of exceptions as needed without having to modify existing code. This will help ensure that your application is always up-to-date and running smoothly.

4. Throw exceptions in your controllers and services

When you throw an exception in your controller or service, it allows NestJS to catch the error and handle it gracefully. This means that instead of having a generic 500 Internal Server Error response, NestJS can provide more specific information about what went wrong. This makes debugging easier and helps ensure that users get the best possible experience when using your application.

Additionally, throwing exceptions in your controllers and services also allows you to create custom error messages for each type of exception. This way, you can give users more detailed feedback on why their request failed, which can help them troubleshoot any issues they may be having.

5. Handle errors with middleware

Middleware is a great way to handle errors because it allows you to catch and respond to any errors that occur in your application. This means that if an error occurs, you can log the error, send an email notification, or even redirect the user to a different page.

Middleware also makes it easy to create custom error handlers for specific types of errors. For example, you could create a middleware function that handles 404 errors by redirecting users to a custom “page not found” page. You could also create a middleware function that handles 500 errors by sending an email notification to the system administrator.

By using middleware for exception handling, you can ensure that all errors are handled properly and that your application remains stable and secure.

6. Don’t forget to log errors

Logging errors helps you to identify and debug issues quickly. It also allows you to track the frequency of errors, which can help you determine if a particular issue is widespread or isolated.

Logging errors should be done in a consistent manner so that it’s easy to search through your logs for specific errors. You should also include as much information as possible about the error, such as the type of error, the stack trace, and any other relevant data. This will make it easier to diagnose and fix the problem.

7. Return meaningful HTTP status codes

When an exception occurs, the client should be able to understand what went wrong and why. By returning a meaningful HTTP status code, you can provide this information without having to write out a lengthy error message. For example, if a user tries to access a resource they don’t have permission for, you could return a 403 Forbidden status code instead of a 200 OK. This way, the client knows that their request was denied due to lack of permissions.

By following this best practice, you can make your API more intuitive and easier to use for clients.

8. Test your error handling code

Testing your error handling code ensures that it is working as expected and catches any errors that may occur. This helps to prevent unexpected behavior in production, which can lead to costly downtime or data loss. Additionally, testing your error handling code allows you to identify potential issues before they become a problem.

To test your NestJS exception handling code, use unit tests to simulate different scenarios and ensure that the correct response is returned for each scenario. You should also consider using integration tests to make sure that all of the components are working together correctly. Finally, be sure to monitor your application’s logs to detect any unexpected errors that may have been missed during testing.

9. Use the built-in logger

The logger is a great way to keep track of errors and exceptions that occur in your application. It allows you to easily identify the source of an error, as well as any related information such as stack traces or other contextual data.

The built-in logger also provides a consistent format for logging errors, which makes it easier to search through logs and quickly find relevant information. Additionally, the logger can be configured to send notifications when certain types of errors occur, allowing you to take immediate action if necessary.

10. Use the ValidationPipe for data validation

The ValidationPipe is a built-in pipe that can be used to validate incoming data. It uses the class-validator library, which provides an easy way to define validation rules for your objects and their properties.

Using the ValidationPipe helps ensure that only valid data is passed into your application. This reduces the chances of errors occurring due to invalid input, as well as making it easier to debug any issues that do arise. Additionally, using the ValidationPipe makes it easier to keep your code clean and maintainable by reducing the amount of manual validation logic you need to write.