Sure! Here's a simple implementation of the Flappy Bird game using JavaScript within a single HTML file:
To play the game, you can copy the above code into a new HTML file (e.g., `flappy_bird.html`) and open it in your smartphone's browser. Tap the screen to make the bird fly (or use the Space key) and avoid crashing into the green obstacles. Your score will be displayed at the top left corner of the screen.