Sure, here's a basic example of a 3D game implemented as a single HTML file using JavaScript and enclosed in script tags:
This is a simple example of a 3D game where a blue square is rendered in the center of the screen using the HTML canvas element. The `startGame` function sets up the canvas and initializes the game loop. The `update` function updates the game state and renders the 3D scene continuously using the `requestAnimationFrame` method.
Note that this code only provides a starting point for a 3D game and can be expanded upon to include more complex features and visual effects.