I've joined the Advent of Code, and I'll be doing it in JS. Got my 2 stars for the day.
For good discipline (or as a handicap), I'm building a halfway-decent set of pages, unit testing framework, and sort of doing things right (good ES6 practices) instead of easy (hack some inline JS in compatibility mode). I'll link it in the sidebar tomorrow, when challenge 1 expires: My Advent of Code
Go on and do it yourself! I say "easy mode is for babies" and make it hard on myself, but really you can do this in anything. There's a perfectly nice Chipmunk BASIC or FreePascal if you're old-school.
Note: The leaderboard reset time is ridiculous, and I don't care about speed-coding or leaderboards. Don't stress about competing for first 100 completions, just do the thing.