Sure! Here's an example of a simple Flappy Bird game implemented as a single HTML file with JavaScript:
To play the game, you can copy the entire code into a single HTML file and open it in a web browser on your smartphone or any other device with a web browser. Tap the screen to make the yellow circle (the bird) jump. Avoid colliding with the green pipes. Your score will be displayed on the top of the screen, and the game will end if you collide with a pipe.