Sure! Here's an example of a simple game about two balls colliding into each other implemented as a single HTML file using JavaScript:
To play the game, open the HTML file in a web browser, and you will see two balls moving horizontally on a canvas. When the balls collide, their directions will reverse.
Please note that this is a basic implementation to demonstrate the concept of the game. You can enhance it by adding more interactivity, levels, scoring systems, etc., as per your requirements.