Sure! Here's a simple example of a 2D platformer shooter game implemented as a single HTML file using JavaScript. Please note that due to the platform's limitations, the game might not be very feature-rich, but it should give you an idea of how to create a basic game structure.
In this game, you control a player character using the left and right arrow keys. Pressing the space bar will shoot bullets from the player's position towards the top of the screen. The game loop constantly updates the game state and renders the current frame on the canvas.