Exception Filter

Exception handling with exception filters

Exception handling is the process of dealing with errors in an app. NestJS provides exception filters to catch unhandled exceptions and return them as an appropriate response. In this lesson, we’ll dive into handling HTTP exceptions using an exception filter and discover how to manage error responses gracefully.

Exception filters

NestJS provides a range of built-in exception filters to handle common scenarios. One notable example is the HttpException filter, which is valuable for managing HTTP-related exceptions like the “404 Not Found” exceptions. This built-in filter allows for the standardized handling of common HTTP errors.

Moreover, NestJS allows us to develop custom exception filters when fine-tuned control over exception handling is required. For instance, a custom exception filter can be designed to tailor the error response according to specific requirements when dealing with authentication errors.

If NestJS can’t find an exception filter corresponding to the thrown exception type, it will invoke the built-in global exception handler. The built-in global exception filter will format and return a proper response for any HttpException. If the exception isn’t HttpException, an internal server error response with the status code 500 will be returned.

Create an exception filter

An exception filter is a class that implements the ExceptionFilter interface and uses the @Catch() decorator. The ExceptionFilter interface requires us to implement the catch method as demonstrated below: