NestJS 在服务类中丢失了 this 内部函数方法的上下文

Question

我有一个带有 monorepo 结构的 nestJS 项目，并且在使用 this 和 context 时遇到了困难。

我有一个应用文件：app.service.ts 和一个通过 Nest CLI 生成的内部库。 app.services.ts的代码逻辑如下：

//import dependencies

@Injectable()
export class AppService implements OnApplicationBootstrap {
  private readonly logger = new Logger('SomeName');

  private readonly ENV_VARIABLE = config.from();

  private ws: WebSocket;

  constructor(
    @InjectRepository(RowEntity) //Repository from TypeORM
    private readonly postgresRepository: Repository<RowEntity>,
    private readonly otherService: LibService, // import from @app/lib
  ) {}

  async onApplicationBootstrap(): Promise<void> {
    await this.loadInitial();
  }

  async loadInitial() {
    this.ws = new WebSocket(url); // standart web socket connection

    const connection = new this.ws() // connection works fine

    addListener(connection, this.logger, this.ProblemSave);  //such as Listener

    /**
     * BUT! 
     * await this.LibService.getMethod(input.toLowerCase()); 
     * works well here!
     */
  }

  async ProblemSave(input: string) {
    /**
     * PROBLEM HERE!
     * NestJS losing context of this keyword when executing via Listener
     */
    const data = await this.LibService.getMethod(input.toLowerCase()); // drops with error, since this undefined
    console.log(data);
    await this.postgresRepository.save(data);
  }

所以我的问题如上所示。我在类服务中有一个函数方法，在 Nest 中创建，它在另一个方法中作为函数调用。但在某种情况下，this 内部类方法工作正常。但是如果我用另一种方法传递它，this 的上下文会丢失，我的函数会失败，this.LibService is undefined 错误。

我应该怎么做才能解决这个问题？

如果有人感兴趣，下面是监听器代码。

export function addListener(
  connection: connectionInterface,
  logger: Logger,
  saveFunc: FunctionInterface,
): void {
  connection.events({}, async (error: ErrnoException, {
    returnValues,
  }: {
    returnValues: ObjectInterface
  }) => {
    if (error) {
      logger.log(error);
      return;
    }

    try {

      //Execution works fine, but fails, because saveFunction doesn't have this context
      await saveFunc({
        input
      });

      logger.log(`Event created with id ${id}`);
      return;
    } catch (e) {
      console.error('ERROR', e);
      logger.log(e);
    }
  })
    .on('connected', (subscriptionId: string) => {
      logger.log(`subscribed to events with id ${subscriptionId}`);
    })
    .on('error', (error: ErrnoException) => {
      logger.log('error');
      logger.log(error);
    });
}

Answer 1

有几种方法，第一个解决方案是构造函数中的bind yow ProblemSave 方法

export class AppService {

  constructor () {
    this.ProblemSave = this.ProblemSave.bind(this);
  }

   ProblemSave () {
     //stuff
   }
}

另一种解决方案是使用箭头函数而不是方法

export class AppService {

  constructor () {}

   ProblemSave  = () => {
     //stuff
   }
}