Interceptors

Server Enviroment
Client Enviroment

Overview

Interceptors can be used to intercept any incoming event/request and outgoing response. They can also change the execution context. Interceptors are executed after guards.

Creating an Interceptor

Interceptors are classes that implement the Interceptor interface. The Interceptor interface has an intercept method that returns a function to be used after the handler method has been executed.

@Injectable()
export class DeliciousMangoInterceptor implements Interceptor {
    public intercept(context: ExecutionContext) {
        console.log('Mango is delicious!');
        return (result: 'yellow' | 'green') => {
            if (result === 'green') {
                console.log('Mango is not ripe yet!');
            } else {
                console.log('Mango is ripe!');
            }
        };
    }
}
typescript

Using an Interceptor

Interceptors can be used at the module, controller or handler level. To use an interceptor, use the @UseInterceptors decorator on the module, controller or handler, and pass the interceptor class as an argument.

NOTE
  • When you specify an interceptor as a class reference, it is instantiated as a singleton by the dependency injection container. This means that the same instance is used for all requests. If you want to use a new instance for each request, you can specify an instance of the interceptor instead of a class reference.
  • If you're using class references, don't forget to add the @Injectable decorator and add the guard to the providers array in the module.
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@Controller()
@UseInterceptors(DeliciousMangoInterceptor) 
export class DeliciousMangoController {
    @UseInterceptors(DeliciousMangoInterceptor) 
    @On('eat')
    public onEat() {
        console.log('Mango is eaten!');
    }
}

@UseInterceptors(DeliciousMangoInterceptor) 
@Module({
    controllers: [DeliciousMangoController],
    providers: [DeliciousMangoInterceptor],
})
export class DeliciousMangoModule {}
typescript

You can also pass an instance of the interceptor instead of a class reference. However, dependency injection will not work for the interceptor instance.

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@Controller()
@UseInterceptors(new DeliciousMangoInterceptor()) 
export class DeliciousMangoController {}
typescript
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Last update at: 2024/04/29 10:15:50