For me personally, it's being able to focus on one language, and one standard library, and be able to re-use that skill-set everywhere. Whether I'm working on

For me personally, it's being able to focus on one language, and one standard library, and be able to re-use that skill-set everywhere. Whether I'm working on a server-side web app, a client side JS framework, a CLI tool or a mobile game, I can use the same language, same libraries, same idioms, but a completely different target platform. In my work I've targeted JS (browser), Neko (server), JS (server), JS (node-webkit), C++, Java and Python - all using the same language / standard library. It means my brain doesn't have to switch gears as often when I need to make something to run on a different platform / technology. Plus there is a huge amount of code re-use you can achieve across platforms. You can get something somewhat similar with JS thanks to Node (targeting client + server + CLI), but I find Haxe a much nicer language to work with - both for Object Oriented style code and more functional style code. The GADTs, "Abstract types", and meta programming (macros) are all features I think Haxe implements in a more well thought out way than other compile-to-JS languages.