Over the past years, I have used Reactive programming every now and then. Let me give you a short description of what reactive programming really is:

Reactive programing says that "instead of executing steps in a synchronous, thread-blocking manner, you do multiple things and then leave them to be."

Let's take a quick example here -- say you want to cook biryani (it's a delicious rice-based dish, native to India). One way to do that would be the old-fashioned synchronous way of waiting for everything in a line:

• get the rice;
• mellow it in warm water;
• prepare the utensils; ...

Here, you'll be exhausted in the end, and just sleep. All the cooking, in vain.

The async., reactive way here will be:

• delegate someone to get the rice; that 'worker' will message you when the rice is here;
• (till then), you prepare the utensils; with your mystical powers, it's happening on its own, and the genie will inform you ...

You can clearly see that the second one is better. It gets the thing done quickly, with less pain and hassle. And here, I very cunningly, described the Pub-Sub model as well. All of this, is reactive programming: waiting for async. data flows.

If you've read any of my answers, you must've realised that I keep on blabbering about messaging queues and whatnot. Well, you can use reactive programming with it, but now reactive functional programming. With JavaScript, you get the best of both worlds.

A place where I used this in production was -- I was making an image verification system; I'll spare you the gory mathematical details, but just to filter the spam, we had to see if it was a face in the first place. Since we had multiple requests streaming in, we pushed it to a queue, and subscribed to its onHaarComplete (it's a preliminary wavelet transform for the Viola-Jones facial detection algorithm) event.

Personally, I am a huge fan of Reactive functional programming. You can throw functions, apply data-reduction algorithms, wait for it (last HIMYM reference, I promise) and what not.

Being someone who has written backends in Ruby as well, this definitely makes life simpler!

I hope this helps! :)