Sure! Here is an example of a simple game implemented as a single HTML file using JavaScript:
This game is a simple one where you control a blue player square using your smartphone's touch or mouse movement. The objective is to avoid colliding with the red enemy square. If the player and enemy squares collide, a "Game Over!" message will be displayed, and the game will reset.
Please note that this is a basic example, and you can customize and expand upon it to make it more interesting or complex.