All of the language features in ES6 / Flow / JSX that Facebook has been pushing through as part of the React ecosystem have been pioneered by Hack/HHVM at Facebook and then ported very closely to the JavaScript ecosystem.

It is available. My understanding is that, unlike PHP, it really only has first-class support on Linux. You can run it on macOS, but you may have to fix some issues yourself.

I've been tempted to use it for things like static website generation, since it has the "XHP" stuff, which is like JavaScript's JSX... and I'd undoubtedly prefer writing code in Hack to writing code in JavaScript.

https://docs.hhvm.com/hack/XHP/introduction

JSX is based on XHP, of course, not the other way around.

The warnings about MacOS are mostly being cautious, as I don't think anyone actually runs it in production.

I work with open source Hack code a lot, and I almost always use the MacOS binaries instead of Linux for development.

For my workflows, it's more that there's two major missing things - I'm not seeing random issues. The big things are:

- a lot of the profiling features are Linux-only

- the mcrouter extension is Linux-only. If you're using memcached, this extension is useful even without mcrouterd, as it provides a true async (Awaitable) client.

That feature is also part of the PHP language. Also as far as I know Hack is available to everyone.