Sure! Here's a simple 3D shooter game implemented as a single HTML file using JavaScript:
This code sets up a basic 3D shooter game where you control a blue player square using the Arrow keys on your smartphone. Pressing the spacebar button will shoot red bullets from the player. The objective is to destroy the green enemy squares that spawn from the top of the canvas. If an enemy reaches the bottom of the canvas, the game is over, and an alert will appear.