Angular 9 - interceptor - what to return if no error in catcherror?

Issue

I have an interceptor in an angular app

the whole idea is that there is a jwt token valid for 30'

• once in a while I get an error from the status code, so I deal with it

• but sometimes, there is no error, so I dont want to throw any exception

since I don't return anything I get this error

You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.

unless I throw fake exceptions like throwError("OK");

here is my intercept function

intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> 
{
    
    return next.handle(request).pipe(catchError(err => 
    {
        const error = (err.error?err.error.message:null) || err.statusText;

        switch (err.status) {
            case 401:
            {
                // token expired -> goto login, dont return error
                this.appService.clearUserSession();
                this.router.navigate(['login']);
                <<<<<<<<<<<<<<< HERE I DON'T WANT TO THROW AN ERROR, WHAT TO RETURN ?
            }
            break;
            case 500:
            {
                return throwError(error);
            }
            break;
            default:
            {
                  if(error!="OK")
                  {
                       return throwError(error);
                  }
                  else
                  {
                       // some errors are "OK", just ignore them
                       <<<<<<<<<<<<<<< HERE I DON'T WANT TO THROW AN ERROR, WHAT TO RETURN ?
                  }
            }
            break;
       }
      
    }))

  }

what do I return in place of <<<<<<<<<<<<<<<<<<<<<<<<<<<< ????

thanks for helping me

Solution

Like the error says, the RxJS catchError operator must return an observable. But when you wish to not throw the error you can use RxJS of function to return a valid notification. It will invoke the next callback of the observable instead of the error.

import { of } from 'rxjs';

intercept(request: HttpRequest < any > , next: HttpHandler): Observable < HttpEvent < any >> {
  return next.handle(request).pipe(catchError(err => {
    const error = (err.error ? err.error.message : null) || err.statusText;
    switch (err.status) {
      case 401: {
        // token expired -> goto login, dont return error
        this.appService.clearUserSession();
        this.router.navigate(['login']);
        return of(error);      // <-- return observable using `of`
      }

      case 500: {
        return throwError(error);
      }

      default: {
        if (error != "OK") {
          return throwError(error);
        }
        return of(error);      // <-- return observable using `of`
      }
    }
  }));
}

Or if you do not wish to call the next callback, you could return EMPTY constant to complete the observable.

import { EMPTY } from 'rxjs';

default: {
  if (error != "OK") {
    return throwError(error);
  }
  return EMPTY;      // <-- complete the observable
}

Answered By - ruth