Am I using Angular 5 http interceptor correctly? - httpclient

Question

I always return http 200 back and define my own error code. If using Promise, I could reject a response which contains customized error. How can I do it using Observable? I do it like this and it works, but is it a correct way?
My interceptor:
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
return next.handle(req).flatMap((event: any) => {
if (event instanceof HttpResponse) {
if (event.body.status) {
if (event.body.status === 'NOK') {
return Observable.throw(event.body);
}
}
}
return Observable.create(observer => observer.next(event));
})}
My provider:
private handleErrorObservable(error: Response | any) {
return Observable.throw(error.message || error);
}
constructor(public http: HttpClient) {
}
signIn(params: any) {
...(some more codes here)
return this.http.post(this.apiUrl + func, requestData, options).map(
(response) => {
//do something with the response
return response;
}).catch(this.handleErrorObservable);
}
My component:
if (form.valid) {
this.auth.signIn(this.login).subscribe(val => {
//console.log(val);
this.navCtrl.setRoot('WebPage');
}, err => {
// error handling here
})
}