RxJS used to encourage monkey patching of operators and helper functions onto the Observable object. However, this has an unfortunate side effect of making the imports available everywhere. Removing an import from one file can inadvertently break code in other files. To alleviate this problem, alternative imports in the form of lettable operators are available since RxJS 5.5.
Let's create an Ionic 2 page that auto-refreshes at regular intervals with a twist: there's also a button for manual refresh which triggers an immediate refresh. We'll implement it in two different ways: with standard JavaScript functions and with RxJS.
Many Angular 2 and Ionic 2 APIs return RxJS observables. To unit test your code that's consuming them, you will need to create your own observable streams with test data. With this approach I wrote tests for code reacting to user's current geolocation.