Sure, here's an example of a simplified version of the Flappy Bird game implemented as a single HTML file with JavaScript:
This code creates a canvas element for the game, defines the game's objects (bird and pipe), handles the game loop, collision detection, and game over condition. The bird can be controlled by pressing the Space key to make it jump. The score is displayed in an alert box when the game is over.
Please note that this is a simplified implementation of the Flappy Bird game, and there might be additional features and improvements that can be made.