Sure, here's a simple example of a 3D shooter game implemented as a single HTML file using JavaScript:
This example sets up a game canvas and creates a player object. The player can move using the arrow keys on a smartphone. The game loop continuously redraws the player's position on the canvas, creating a basic 2D shooter game experience. Of course, for a complete 3D shooter game, additional graphics rendering and game mechanics would need to be implemented, but this gives you a starting point to build upon.