How to resolve findIndex is not a function error in Typescript?

Question

In my Angular app, I am storing an array of Message objects within a Conversation object.

I was able to add a new Message to a hard-coded Conversation with the below code:

private _conversations = new BehaviorSubject<Conversation[]>([]);

get conversations() {
    return this._conversations.asObservable();
}

addMessageToConversation(conversationId: string, message: string) {
    return this.conversations.pipe(
      take(1),
      tap(conversations => {
        const updatedConversationIndex = conversations.findIndex(convo => convo.id === conversationId);
        const updatedConversations = [...conversations];
        const convoToUpdate = updatedConversations[updatedConversationIndex]; 
        convoToUpdate.messages.push(
          new Message(
            Math.random().toString(),
            message,
          )
        );
        this._conversations.next(updatedConversations);
      })
    );
  }

I made the below changes to this method so that I could update the object in a Firebase DB:

addMessageToConversation(conversationId: string, message: string) {
    let updatedConversations: Conversation[];
    return this.conversations.pipe(
      take(1), switchMap(conversations => {
        console.log(conversations);
        const updatedConversationIndex = conversations.findIndex(convo => convo.id === conversationId);
        updatedConversations = [...conversations];
        const convoToUpdate = updatedConversations[updatedConversationIndex];
        convoToUpdate.messages.push(
          new Message(
            Math.random().toString(),
            message,
          )
        );
        return this.http.put(
          `myUrl/conversations/${conversationId}.json`,
          { ...convoToUpdate, id: null }
        );
      }), tap(() => {
        this._conversations.next(updatedConversations);
      })
    );
  }

But now when I call this method, I get this console error:

conversations.findIndex is not a function

This error is in relation to this line of code:

const updatedConversationIndex = conversations.findIndex(convo => convo.id === conversationId);

Also, when I console.log(conversations) inside switchMap, this is logged:

{id: "-M52u0Fwdt5a9xE0wwCk", userId: "user3", mechanicId: "user2", messages: Array(1)}

Can someone please tell me why this is happening, & what changes are required to get it working?

findIndex works for array only, check developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…. — Piyush Jain
– Piyush Jain, Commented Apr 17, 2020 at 11:21

Suren Srapyan · Accepted Answer · 2020-04-17 11:06:06Z

1

If you are sure that conversations is an array, you can just set the type of it to any

...
switchMap((conversations: any) => {
     const updatedConversationIndex = conversations.findIndex(convo => convo.id === conversationId);
     updatedConversations = [...conversations];
...

Or even better create a type for it.

answered Apr 17, 2020 at 11:06

Suren Srapyan

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7 Comments

user9847788 Over a year ago

Thanks for your answer, but this code gives me the same error. I am showing what conversations is in my question aboce now

Suren Srapyan Over a year ago

So that is an object, not an array. Maybe you want to use findIndex on the messages?

user9847788 Over a year ago

Yep, so what I want do here is add / push a new Message to the Message array inside Conversation

Suren Srapyan Over a year ago

You can directly use conversations.messages because you have already the the only one via take(1). No more filtering is needed

user9847788 Over a year ago

OK, I will try to get my code working based on this. Is it possible for you to show how it should be done above in your answer?

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