I participated two times in the JS1K competition. It runs yearly, usually in or around February / March. The core rule is no externals. You must submit a self-contained demo in 1024 bytes of pure JS, which in turn may use various web technologies.
A view of a passing procedural landscape from a train window in 1kb of javascript.
JS1k post mortem – Train Window
A Minecraft landscape renderer in 1k javascript showing water, hills, trees and fog.