Not JavaScript, but there was actually a 4kb version of Minecraft for a contest: https://archive.org/details/Minecraft4K
Due to the way Java4k works (your entry is measured by compressed jar size), every byte can fit a little more than the previous one, so 2000 bytes is actually less than half the allotted space.
He didn't finish his game in time though: https://twitter.com/notch/status/1039836244065378304 :)