How to throw error from RxJS map operator (angular)

Question

I want to throw an error from my observable\'s map operator based on a condition. For instance if correct API data is not received. Please see the following

Answer 1

If you feel like throw new Error() seems un-observable-like you can use return throwError(...) with switchMap instead of map (the difference being switchMap has to return a new observable instead of a raw value):

// this is the import needed for throwError()
import { throwError } from 'rxjs';


// RxJS 6+ syntax
this.httpPost.pipe(switchMap(res => { 
   if (res.bearerToken) {
      return of(this.saveJwt(res.bearerToken)); 
   } 
   else {
      return throwError('Valid token not returned');  // this is 
   }
});

or more concisely:

this.httpPost.pipe(switchMap(res => (res.bearerToken) ? 
                                    of(this.saveJwt(res.bearerToken)) : 
                                    throwError('Valid token not returned')
));

The behavior will be the same, it's just different syntax.

You're literally saying 'switch' from the http observable in the pipe to a different observable, which is either just 'wrapping' the output value, or a new 'error' observable.

Don't forget to put of or you'll get some confusing error messages.

Also the beauty of 'switchMap' is that you can return a whole new 'chain' of commands if you wanted to - for whatever logic needs to be done with saveJwt.