Does anyone have ideas for small projects I can complete that will really drive home the importance/benefits of functional programming?
For example, a counter that increments per click:
initApp = { counter: 0 };
stepApp = (action, oldApp) => oldApp.counter + 1;
viewApp = (app) => `<p>Clicks so far: ${app.counter}</p>`;
currentApp = reduce(stepApp, initApp, mouseClicks);
currentHtml = map(viewApp, currentApp);
Though it's possibly hard to appreciate this until you've battled it out in the trenches with an abstraction that isn't so simple, especially on a large, complex app.
I personally found Redux (w/ React) immediately accessible and think it's a good place to start, especially if you're already coming from React or you want to reap the benefits without leaving Javascript. I'd feel really comfortable using Redux on any team project that was already using React and some other Flux'y implementation.
I've also been learning Elm this past week though it's taking me far longer to become productive since there are fewer resources and I have no ML experience. I've managed to create a simple Spreeder.com-style speed-reader (https://www.danneu.com/elm-speed-reader/), and if you look at the source code (https://github.com/danneu/elm-speed-reader/blob/master/Machi...), you can see that it's not much different from the counter-app example I pitched above where the `update` function reduces across a stream of actions including button clicks and the tick. (Disclaimer: I'm an Elm noob)
In my experience I've been able to model any conceivable interactions with a website using this model.
It helped me a lot to understand the practical side of functional programming.
For a book that maximizes the utility of functional programming in your everyday life I would recommend "functional javascript" by the famous author of underscore.js
From my experience with Haskell, on a practical level, I think it really comes down to a guarantee that you will not be able to mess the code up beyond a certain extant.
I am not really sure if it should be attributed to the type system or to functional programming in general. A functional programming language require a really good type system, because you need it maintain sanity with you have to chain together functions a lot more than you do in an imperative language. So I think it has to be a mix of both.
But the "FP" part is only tangentially the point unless you take FP to mean "pure functional programming", ie, just a lambda calculus.
Having the ability to write "map" and "filter" in your programming language doesn't really do much for you in practice. Believing otherwise is why people thought FP users were nuts for a long time.