Struggling with unexpected behavior when converting JSON to interface in an HTTP response casting

My angular client is sending a get request to a server, expecting an observable with an array of objects. However, I am encountering an issue as typescript does not allow me to cast the JSON response to my desired interface.

The JSON object sent by the server looks like this:

export interface Message {
    title: string;
    body: string;
}

I want to cast the JSON body to the following interface, which should contain an array of objects:

export interface ICommonGameCard {
    id: string;
    pov: POVType;
    title: string;
    image_pair?: ICommonImagePair;
    best_time_solo: number[];
    best_time_online: number[];
}

export enum POVType{Simple, Free};

This is the service responsible for handling the requests:

public getGameCards(povType: POVType): Observable<ICommonGameCard[]> {
    return this.http.get<ICommonGameCard[]>(this.BASE_URL + this.GET_ALL_CARDS_URL)
        .pipe(
          map((res: Response) => return <ICommonGameCard>res.json().body),
          catchError(this.handleError<Message>("getUsernameValidation")),
      );

}

Unfortunately, my current approach is not working. I am trying to cast the JSON response to the message Interface and access the body where there should be an array of ICommonGameCard.

The error I am facing is:

[ts]
Argument of type 'OperatorFunction<Response, ICommonGameCard>' is not assignable to parameter of type 'OperatorFunction<ICommonGameCard[], ICommonGameCard>'.
  Type 'Response' is missing the following properties from type 'ICommonGameCard[]': length, pop, push, concat, and 26 more. [2345]

Can anyone point out what's wrong with my syntax?

Answer №1

export interface Message {
    heading: string;
    content: ICommonGameCard[];
}
public retrieveGameCardsByType(userType: UserType): Observable<ICommonGameCard[]> {
    return this.http.fetch<Message>(this.BASE_URL + this.GET_ALL_CARDS_URL)
        .pipe(
          mapping((message: Message) => message.content),
          handlingError(this.handle<Message>("fetchUserDetails"))
      );
}

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