Sure, here's an example of a game implementation in a single HTML file using JavaScript. Note that this is a simple demonstration, and you can customize it further to add more features or fine-tune the gameplay as per your requirements.
Please copy the code below and save it as a .html file to play the game:
In this game, the player controls a black square using arrow keys on a smartphone to avoid sharks (gray squares). If the player collides with any shark, the game will show a "Game Over" alert. The game uses JavaScript to handle player movement, collision detection, and rendering the game objects on an HTML5 canvas.