I wanted to build my game from scratch, without engines or libraries. I ended up not using any assets either, mostly to save time looking for them and managing them. Instead of assets I just used emoji, which are really easy to work with (at least in the canvas API), since I can use the emoji directly in the code. The big downside is that the look of the game does change between different platforms.
There's a bunch more smaller hacks that I use to save time. If there's other plain html5 devs out there that are interested, I'm happy to share some of these.
The game is here: