Combine Values of One Observable with RxJS scan

All of the combination operators take two or more observables as input. These operators may also be alternatively called "vertical combination operators", because of how they work in a marble diagram. Next, we will learn about scan(), which is an important "horizontal combination operator".

🚨 Since we are importing interval from RxJS, we don't need to preface our Observables with Rx.Observable. You can no longer .{operator}, you need to .pipe({operator}) instead. To link together multiple Observables and Operators, the method is a bit different. You call zip first, then list your Observables, your functions, then pipe your Operators.