Sure! Here's an example of a simple Flappy Bird game implemented as a single HTML file using JavaScript:
In the above code, the game consists of a flappy bird represented by a yellow square moving downwards due to gravity. The player can make the bird jump by touching the screen (in case of smartphones) or clicking the canvas (on desktop). The score is displayed at the top left corner of the canvas. The game loop continuously updates the bird position, clears the canvas, and redraws the bird and score. The game continues until it's closed.
Please note that this is a simplified implementation of the game, and you can further enhance it by adding pipes, collision detection, and game over conditions.