Last year the company I work runned their own internal hackathon, trying to find and map shadow IT developers.

To finish the registration, developers should submit an html game (like snake, sudoku). The rules were:

• Only one html file; and
• Pure JavaScript (no external dependencies, assets, libs).

Live demo here!

• Since there were no rules for CSS, every animation uses it.
• Works on IE, Edge, Firefox and Chrome.
• For the fireworks animation, I used the Eddie Lin's Pure CSS Fireworks.
• The algorithm for board generate was based on The ANZAC's code available here.

• http://delarco.com.br/games/sudoku-js (live demo)
• https://www.codeproject.com/Articles/23206/Sudoku-Algorithm-Generates-a-Valid-Sudoku-in
• http://jsfiddle.net/elin/7m3bL (Pure CSS Fireworks)