Filter Hierarchy

Preview — 3 of 10 questions

What advantage does registering a global filter with the APP_FILTER token have over app.useGlobalFilters(new MyFilter())?

javascript

import { Module } from '@nestjs/common';
import { APP_FILTER } from '@nestjs/core';
import { AllExceptionsFilter } from './all-exceptions.filter';

@Module({
  providers: [{ provide: APP_FILTER, useClass: AllExceptionsFilter }],
})
export class AppModule {}

AIt runs filters faster at runtime

BThe filter is instantiated by the DI container, so it can inject providers like a logger or config service

CIt disables all other filters in the app

DIt only works for WebSocket gateways

In a global catch-all filter that needs Nest's default behavior as a fallback, what must you provide if extending BaseExceptionFilter without DI?

javascript

import { Catch, ArgumentsHost } from '@nestjs/common';
import { BaseExceptionFilter, HttpAdapterHost } from '@nestjs/core';

@Catch()
export class GlobalFilter extends BaseExceptionFilter {
  constructor(adapterHost: HttpAdapterHost) {
    super(adapterHost.httpAdapter);
  }
  catch(exception: unknown, host: ArgumentsHost): void {
    super.catch(exception, host);
  }
}

AThe HttpAdapterHost (or applicationRef) so the base class can send a response

BNothing — it works automatically

CA Redis client

DA custom RxJS scheduler

How do you customize error handling for a @WebSocketGateway?

javascript

import { Catch, ArgumentsHost } from '@nestjs/common';
import { BaseWsExceptionFilter, WsException } from '@nestjs/websockets';
import { Socket } from 'socket.io';

@Catch(WsException)
export class WsExceptionFilter extends BaseWsExceptionFilter {
  catch(exception: WsException, host: ArgumentsHost): void {
    const client = host.switchToWs().getClient<Socket>();
    client.emit('error', { message: exception.message });
  }
}

AUse the same BaseExceptionFilter unchanged

BImplement a filter that handles WsException and uses host.switchToWs() to access the client

CWebSocket errors cannot be filtered in NestJS

DThrow HttpException from the gateway

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