A while ago, 2008-ish by the timestamps on the original files, I was reading about prototypical inheritence and figured I'd try it out. I'd also been wanting to try my hand at creating a video game for awhile. I like Tetris so it seemed like as good a starting point as any. I took a weekend and got the major functionality in there, and then spent another three weeks off-and-on "polishing" it before I got sidetracked by real life. It looks like I did another update in ~2011; neither attempt utilized a build process, so everything was just jammed into "engine.js", including what passes for unit tests.
You can play the game here, if you want.