Typescript Generics and rxjs map

Question

How can we write a generic RXJS map function, and use it like an error handler applied to an Angular Http observable ?

I have tried :

registerUser(user: CreateUserAPI) {
  interface res  {
    session_key?: string;
    result?: string;
    error?: string;
  }

  return this.http
    .post<res>(`${API_URL}/api/customer/register`, user)
    .pipe(catchError(this.handleError), map(this.captureError));
}

captureError<T>(res: T): T {
  if (res.error) { // <== TS ERROR : Property 'error' does not exist on type 'T'
    Raven.captureMessage(res.error);
  }
  return res;
}

test(){
    let user : any
    this.registerUser(user).subscribe(res => {
      res.error // no error
    })
  }

But TS is returning the error : Property 'error' does not exist on type 'T'

My goal is to keep the typing of my observable when I subscribe to it later (test() method)

YD1m · Accepted Answer · 2018-03-28 10:31:48Z

1

You can set that your generic type extends interface with error property:

interface ErrorObj {
  error: string;
}

captureError<T extends ErrorObj>(res: T): T {
  if (res.error) {
    Raven.captureMessage(res.error);
  }
  return res;
}

answered Mar 28, 2018 at 10:31

YD1m

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