Sure, here's an example of a simple game implemented as a single HTML file using JavaScript:
This game is a simple emoji matching game on a smartphone. When you click on an emoji, it checks if it matches the previously clicked emoji. If the emojis match, it shows a congratulations message; otherwise, it shows an "Oops! Try again" message.
You can modify this code further to enhance the game mechanics, add scoring, or style the elements to your liking.