I typed this in from here. Thanks Marijn.
git clone https://github.com/mikew1/a-platform-game
open game.html in browser.
Use arrow keys to move.
The game comes in two versions. In 80's style with DOM display, and one with html canvas.
You can plug in which display you want, or even both at the same time.
DOM display version:
With HTML Canvas instead:
To switch between DOM and Canvas display, open game.html in text editor.
Comments there explain what to change.
You can even run both at once if you want.
Hmm... javascript.