Haven't noticed that until now, but there's controller support. How did you manage to do that on a web page??
It's built with SDL2 and Emscripten, which provides the same interface for doing it on web as with desktop :) They do it through the HTML5 Gamepad API: https://developer.mozilla.org/en-US/docs/Web/API/Gamepad_API/Using_the_Gamepad_A...