Pong is one of the oldest video games, but I made this version using JavaScript during my senior year of high school. It's implemented similarly to my Snake game; the updates some values, such as the position of the paddles, every frame based on user input, and then updates a canvas every frame based on those values. My code is below, but I have a full page version as well. Just hit the play button above the code to start.
The default controls are W and S for player one and I and K for player two, but you can change them, along with some other settings, by clicking on the "settings" button. You can also pause the game with the spacebar.