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Quake-like game made with JavaScript takes up just 13KB of storage
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
The game also requires a renderer (browser) to play.
I think what they did is impressive but the claim about the size feels like taking source code and saying "look how small on disk it is"
It is js, it is always source code.
Except if it's minified for production.
That is still source code, obfuscated but still source code.
Not sure about GreaseMonkey, but V8 compiles JS to an IL.
Nodejs has an emit IL debugging feature to see the emitted IL code.