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The "Challenge 9: Observables" Lesson is part of the full, Functional-Light JavaScript, v2 course featured in this preview video. Here's what you'd learn in this lesson:

In this challenge, students program a countdown timer using observables.

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Transcript from the "Challenge 9: Observables" Lesson

>> Kyle Simpson: So I wanted to give you a very brief opportunity to practice with it. You don't actually need to do any real RX programming. But in EXERCISE 9, you need to do the functional programming part attached to the list. So if you open up the Read Me, you'll see that it says, there's the fix solution works but the exercise does not work.

[00:00:23] And it gives you very specifically what you need to add in. You need to implement a function and then adapt it to the stream. So we'll give you probably a few minutes to try your hand at that. It's really actually only about two or three lines of code, so there's not a lot to do here.

[00:00:38] Well I'll give you a few minutes to familiarize yourself with that and then we'll talk about that solution.