Angular 向处理可观察流的函数添加布尔变量

我有一个函数，它接受线程的参数ID。它处理线程流以确定此ID是否与线程匹配

getThreadFromSubscription(threadId: string): Observable<Thread> {
return this.threads
  .filter((threadDictionary: { [key: string]: Thread }) => {
    return Object.keys(threadDictionary).some((key) =>
      threadDictionary[key].id === threadId);
  })
  .map((threadDictionary: { [key: string]: Thread }) => {
    for (let key in threadDictionary) {
      if (threadDictionary[key].id === threadId)
      {
        return threadDictionary[key];
      }
    }
  }).first();
}

我想向这个函数添加一个布尔变量，以便知道相应的线程是否存在。 如果相应的线程不存在，“newThread”变量将为true。 我尝试过这个，但是当threadID不存在时，它就不起作用了。我的布尔变量“newThread”未设置为true：

addNewMessage(objMessage: any) : void {
this.getThreadFromSubscription(objMessage.id)
  .subscribe((thread: Thread) => {
    if(thread !== undefined) {
      this.newThread = false;
    }
    else {
      this.newThread = true;
    }
  });

if(this.newThread === false )
{
  this.getThreadFromSubscription(objMessage.id)
    .subscribe ((thread: Thread) => {
      console.log("id: tRev");

      if(thread!== undefined) {
        objMessage.thread = thread;
      }
      objMessage.date = moment().toDate();

      const newMessage = new Message(objMessage);

      thread.messages = Observable.of([newMessage]);

      thread.messages.last().subscribe((message) => {
        [thread.lastMessage] = message;
      });

      this.addMessage(newMessage);
    });
}
else
{
  console.log("id: flo");
  const flo: User      = new User(objMessage.author, objMessage.site);
  const newThread: Thread = new Thread(objMessage.id, [flo]);
  const newMessage = new Message(objMessage);

  objMessage.date = moment().toDate();

  newThread.messages = Observable.of([newMessage]);

  newThread.messages.last().subscribe((message) => {
    [newThread.lastMessage] = message;
  });

  objMessage.thread = newThread;

  this.addMessage(newMessage);
  this.addThread(newThread);
}
}

您知道如何添加一个变量来判断给定的id是否已经存在吗

addNewMessage(objMessage: any) : void {
this.getThreadFromSubscription(objMessage.id)
  .subscribe((thread: Thread) => {
    if(thread !== undefined) {
      this.newThread = false;
    }
    else {
      this.newThread = true;
    }
  });

if(this.newThread === false )
{
  this.getThreadFromSubscription(objMessage.id)
    .subscribe ((thread: Thread) => {
      console.log("id: tRev");

      if(thread!== undefined) {
        objMessage.thread = thread;
      }
      objMessage.date = moment().toDate();

      const newMessage = new Message(objMessage);

      thread.messages = Observable.of([newMessage]);

      thread.messages.last().subscribe((message) => {
        [thread.lastMessage] = message;
      });

      this.addMessage(newMessage);
    });
}
else
{
  console.log("id: flo");
  const flo: User      = new User(objMessage.author, objMessage.site);
  const newThread: Thread = new Thread(objMessage.id, [flo]);
  const newMessage = new Message(objMessage);

  objMessage.date = moment().toDate();

  newThread.messages = Observable.of([newMessage]);

  newThread.messages.last().subscribe((message) => {
    [newThread.lastMessage] = message;
  });

  objMessage.thread = newThread;

  this.addMessage(newMessage);
  this.addThread(newThread);
}
}