Reactive programming

Here's a term I hadn't seen before: reactive programming. Reactive programming is a declarative style in which relationships between values are defined, then changes to one value propagate to the other. A data flow graph is created, in other words. I've been stumbling towards this in Decl, of course, but here's Elm, a type-safe functional reactive programming language that compiles to JavaScript.

Apparently, there's nothing that can't be done in JavaScript these days.

I personally find this code nearly unreadable (I'm sure I'd improve with some practice), but the notion of declarative specification of JavaScript I see in the examples is utterly enthralling.