auth-interceptor.ts

@Injectable()
export class AuthInterceptor implements HttpInterceptor
{

    constructor(private _router: Router) { }


    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>>
    {
        let token = localStorage.getItem('api-token');

        if (token) {
            req = req.clone({
                setHeaders: {
                    'api-token': token
                }
            } );
        }

        return next.handle(req).catch(err => {
            console.log(err);
            if (err.status === 401) {
                if (err.error.message == "Token is exp") {
                    //Genrate params for token refreshing
                  let params = {
                    token: token,
                    refreshToken: localStorange("refreshToken");
                  };
                  return this.http.post('localhost:8080/auth/refresh', params).flatMap(
                    (data: any) => {
                      //If reload successful update tokens
                      if (data.status == 200) {
                        //Update tokens
                        localStorange.setItem("api-token", data.result.token);
                        localStorange.setItem("refreshToken", data.result.refreshToken);
                        //Clone our fieled request ant try to resend it
                        req = req.clone({
                          setHeaders: {
                            'api-token': data.result.token
                          }
                        });
                        return next.handle(req).catch(err => {
                          //Catch another error
                        });
                      }else {
                        //Logout from account
                      }
                    }
                  );
                }else {
                    //Logout from account or do some other stuff
                }
            }
            return Observable.throw(err);
        });

      
    }
}

For anyone trying to do this with later Angular versions, this is working for me.

   intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        return next.handle(req).pipe(
            catchError(e => {

                console.log("in catch error: " + e);
                if (e.status === 401) {
                    let refreshToken = this.store.getRefreshToken();

                    return this.authenticationService.loginWithRefreshToken(refreshToken).pipe(
                        flatMap(auth => {
                            this.store.setAuthTokens(auth.accessToken, auth.refreshToken);

                            req = req.clone({
                                setHeaders: {
                                    Authorization: "Bearer " + auth.accessToken
                                }
                            });

                            return next.handle(req);
                        })
                    );
                }
                return next.handle(req);
            })
        );
    }

Thank you. Your save my life in 2022 :)

@knowncolor also saved 2022 ☺