Provided 'undefined' where stream was expected

Question

I am trying to send chained http requests using Rxjs, but I am getting this error...

Error: Uncaught (in promise): TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable. TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.

I want to get location object from my API, then I want to get latitude and longitude based on location.address.

declare const require : any;

@Injectable()
export class GoogleMapLocationResolver implements Resolve<{location: Location, longitude: number, latitude: number }> {

constructor( private locationService: LocationService, 
             private route: ActivatedRoute, 
             private router: Router){}

resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): {location: Location, longitude: number, latitude: number } | Observable<{location: Location, longitude:number, latitude: number }> | Promise<{location: Location, longitude: number, latitude: number }> {

    let geocoder = require('geocoder');

    return this.locationService.getLocation(route.params['id']).map(
        (response: Response)=> { return response.json() }
    ).mergeMap(location => geocoder.geocode(location.address, function(err, data){
        let latitude
        let longitude
        if(data.status === 'OK'){
            console.log('Status ok: ')
            console.log(data)
            let results = data.results;
            latitude = results[0].geometry.location.lat;
            longitude = results[0].geometry.location.lng;
            console.log(latitude); // PRINTS CORRECT
            console.log(longitude); // PRINTS CORRECT
        }                  
        return {location, longitude, latitude};
    })).catch(error => {
        this.router.navigate(['/not-found'])
        return Observable.throw(error);
    })  
  }
}

NOTE: Whats very weird is that after this error, console prints latitude and longitude correct! ('// PRINTS CORRECT' comment)

EDIT: Yep my mistake, I declared variables in if, but that was not a problem at the end. Posting solution soon.

Answer 1

I solved it... Problem is that geocoder.geocode() function has no return value, while mergeMap() is expecting an Promise,Observable etc, geocoder.geocode() returned undefined. My solution is to wrap this function with Promise.

    declare const require : any;

        @Injectable()
        export class GoogleMapLocationResolver implements Resolve<{location: Location, longitude: number, latitude: number }> {

        constructor( private locationService: LocationService, 
                     private route: ActivatedRoute, 
                     private router: Router){}

        resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): {location: Location, longitude: number, latitude: number } | Observable<{location: Location, longitude:number, latitude: number }> | Promise<{location: Location, longitude: number, latitude: number }> {

            let geocoder = require('geocoder');

            return this.locationService.getLocation(route.params['id']).map(
                (response: Response)=> { return response.json() }
            ).mergeMap( location => new Promise<any>((resolve, reject) => {geocoder.geocode(location.address, function(err, data){
                let latitude
                let longitude
                if(data.status === 'OK'){
                    console.log('Status ok: ')
                    console.log(data)
                    let results = data.results;
                    latitude = results[0].geometry.location.lat;
                    longitude = results[0].geometry.location.lng;
                    console.log(latitude); 
                    console.log(longitude); 
                }                  
                resolve({location, longitude, latitude}(;
    })
            })).catch(error => {
                this.router.navigate(['/not-found'])
                return Observable.throw(error);
            })  
          }