如何从Typescript中的另一个类访问方法？

Question

我有2个服务文件，我正试图从另一个文件的for循环中的1个服务文件访问方法，但我得到Cannot read property of undefined error。在以下实现中，我只想将第一个服务文件中的值返回到包含publish方法的第二个服务文件中。如何解决此问题？

这是我的第一个service.ts文件

@Injectable()
export class MessageService {
  constructor(
    private readonly messagePublishService: MessagePublishService,
  ) {}

  message = new ProductMessage();
  publishMessages(productEvent: ProductEvent): Observable<any> {

    var source: string;
    let sourceArn = this.configService.get(source);

    const url = this.configService.get('SITEMAP_ENDPOINT');
    const urls = [url + '/sitemap/retrieve/ide', url + '/sitemap/retrieve/tpd'];
    try {
      for (let i = 0; i < urls.length; i++) {
        return https.get(urls[i], res => {
          res.on('data', function(chunk) {
            json += chunk;
          });
          res.on('end', function() {
            const result = JSON.parse(json);
            getProductCodes(productEvent, result, this.messagePublishService);
          });
        });
      }
    } catch (err) {
      console.error(err);
    }
  }
}

function getProductCodes(
  productEvent,
  result,
  messagePublishService: MessagePublishService,
) {
  const splitCodes = productEvent.productCodes.split(',');

  for (let i = 0; i < result.length; i++) {
    for (let j = 0; j < result[i].products.length; j++) {
      if (
        productEvent.productCodes.length !== 0 &&
        productEvent.productCodes !== undefined
      ) {
        for (let k = 0; k < splitCodes.length; k++) {
          if (result[i].products[j].productCode === splitCodes[k]) {

            messagePublishService.publish(           -----------------> TypeError: Cannot read property 'publish' of undefined
              this.sourceArn,
              result[i].products[j].productCode,
            );
          }
        }
      }  
    }
  }
}

这是第二个服务文件，其中包含我要在第一个服务文件中访问的publish method

@Injectable()
export class MessagePublishService {

  constructor(private readonly configService: ConfigService) {}

  async publish(source: string, message: ProductMessage) {
    let messageString = JSON.stringify(message);

    console.log(
      'MessagePublishService.publish - entry: %s, %s',
      source,
      messageString,
    );
    let sourceArn = this.configService.get(source);


    // Create publish parameters
    var params = {
      Message: messageString /* required */,
      TopicArn: sourceArn,
    };

    let messageId: string = 'NULL';

    console.log('MessagePublishService.publish - exit');
  }
}