Sure! Here's an example of a simple RPG game implemented as a single HTML file using JavaScript:
In this game, you start with a basic weapon and have to defeat enemies to level up and unlock stronger weapons. You can tap/click on the enemies to attack them and reduce their health. When an enemy's health reaches 0, it resets and a new enemy appears. The player's level and current weapon are displayed on the screen.
You can further enhance this game by adding more features like experience points, a health bar, different enemy types, and more advanced player/enemy behavior. However, the provided code should give you a basic understanding of how the RPG game mechanics can be implemented in a single HTML file using JavaScript.