How use async service into angular httpClient interceptor

Question

Using Angular 4.3.1 and HttpClient, I need to modify the request and response by async service into the HttpInterceptor of httpClient,

Example for modifying the requ

Answer 1

I think that there is a issue about the reactive flow. The method intercept expects to return an Observable and you have to flatten your async result with the Observable returned by next.handle

Try this

intercept(req: HttpRequest, next: HttpHandler): Observable> {
      return this.asyncService.applyLogic(req).mergeMap((modifiedReq)=> {
        const newReq = req.clone(modifiedReq);
        return next.handle(newReq);
    });
}

You could also use switchMap instead of mergeMap