Sure, here's a simple example of an FPS shooter game implemented as a single HTML file with JavaScript:
This code sets up a simple 2D canvas where you can control a player square using the arrow keys on a smartphone. The objective is to avoid colliding with a randomly moving red circle (enemy). If the player and enemy collide, the game ends, and the page reloads.
Please note that this is a very basic implementation and can be expanded upon to create a more advanced FPS shooter game.