Angular2 Query Params Subscription Fires Twice

Question

Trying to handle an OAuth login scenario where if the user lands on a page with authorization_code in the query string, we process the token and continue

Answer 1

I guess that's by design.

queryParams is the BehaviorSubject

As you can see in the docs

One of the variants of Subjects is the BehaviorSubject, which has a notion of "the current value". It stores the latest value emitted to its consumers, and whenever a new Observer subscribes, it will immediately receive the "current value" from the BehaviorSubject.

As workaround you can use debounceTime operator as follows:

import 'rxjs/add/operator/debounceTime';

this._route.queryParams
  .debounceTime(200)
  .subscribe(params => {
    console.log(params);
  });