This is a REPL for Lua. Press the button to execute the code in the editor below. You can also modify the code and run it again.
The stuff you see in the example above works, which includes using JavaScript objects from Lua as if they were Lua objects, calling the DOM, callbacks into Lua, etc. And as mentioned on the main page, this uses the compiled Lua VM, so it includes all the normal Lua languages features, and it's compiled into asm.js so it can have reasonable performance.