Instructor: 0:00 Whenever I have to build a new feature or I get a requirement specification, the decision of whether to use RxJS depends on two things for me. Do I need to worry about timing? An example can be as simple as, does it involve async operations? Or even as straightforward as, we need to wait three seconds before making an HTTP request.
0:20 The second question I ask myself is, do we need to coordinate a lot of events that might be of different types like clicks or HTTP requests or even setTimeouts? Again, an example can be, wait for the user to click login then make a post request then when that's done, we direct to the account page.
0:40 To even more complex examples like building a typeahead component where we need to coordinate the user hitting the keyboard with how much time has passed since the last keystroke with making a request to the server to search.
0:53 This is the app we'll be working with. When we click these buttons, we trigger some tasks in the background. Imagine slow HTTP request if you want.
1:03 Our first requirement that we need to build straightaway is to show a loading spinner at the bottom of the app anytime there are any tasks happening in the background. We have a counter here that shows us how many of these tasks are happening at any point in time.
1:18 When we start some tasks, we notice it goes up and then it goes back down again as they start to finish. This indicator is only for explanation purposes here, so you get an idea of what is happening in the background. We're going to solve the problem as if this doesn't exist at all. This requirement is time-based.
1:37 We don't know how long the loader is going to be on the screen, but it will be there for some time, that's for sure. It does involve coordinating different events. We need to coordinate all events happening in the background. I'd say it's a perfect fit for an RxJS Reactive-based solution.
1:53 As with everything in software development, if you build something simple, the case for using RxJS isn't that big, but the decisions you make early will have a compound effect the more your app grows.
2:03 The moment you introduce the concept of time in an app, however simple it may be initially, there's a chance that future requirements will build on that concept and you'll have ever more complex scenarios where you have to consider time, as we shall see.