I got an error trying to play the web version in Firefox: ‘abort(114). Build with -s ASSERTIONS=1 for more info.’
It worked in the Chrome browser though.
I played a match and think it would be nice to have either a start-instruction or the game (the timer) would start automatically. I needed a few moments until I found the spacebar had to be pressed.
Maybe you can make the pads a bit faster, so the match can last longer. The ball would increase its speed over time.
It would also be cool, if you could add a few more options for colors for pads and ball. Generally that is a nice feature.
Looking forward, what you will add to really make it differ from the usual classical Pong. Defence mode was definitly one of them. An online multiplayer mode would be perfect but I know it is harder to implement than to think about it.