[MrBuddyCasino]

Facebook is doing something that enables better IDE support for JS, so static typing isn't absolutely required, it just makes it a lot easier. I forgot the projects name though, the IDE part was also not open sourced back then.

[feedjoelpie]

Their optional typing for JS is called Flow, and they've open sourced an IDE of sorts (a suite of Atom plugins) called Nuclide (http://nuclide.io/).

[MrBuddyCasino]

That was the one, thanks.

[rejschaap]

I have never seen anyone successfully bolt type-checking onto an existing language. It is always painful to use. It usually requires ugly added syntax and you need a special compiler if the language isn't flexible enough.

Why not just use a different language altogether? One that was designed with static type checking from the ground up?

Maybe Facebook likes the pain, they also pushed PHP further than anyone else was willing to. Burning insane amounts of resources with a somewhat disappointing result.