NestJS interceptors: Guide and use cases

NestJS interceptors are powerful tools in the request-response pipeline, allowing developers to manipulate requests and responses within a NestJS application. They are class-annotated with injectable decorators and implement the NestInterceptor interface, featuring methods such as intercept, which processes requests before they reach a controller, and handleRequest, which manages responses post-controller processing. Interceptors can be used for various purposes, including logging, data validation, authentication and authorization, and exception mapping. Custom interceptors can be created and applied at different levels—globally, controller-scoped, or method-scoped—using decorators like @UseInterceptors. By providing direct access to the request before it reaches the route handler and the ability to mutate responses, interceptors enhance the scalability, efficiency, and security of NestJS applications. They can log request details, validate incoming data, ensure proper authorization by checking tokens, and even override default exception handling. This functionality makes interceptors a valuable asset in developing robust backend applications.