Sure! Here's an example of a simple shooter game implemented as a single HTML file using JavaScript:
This code creates a simple shooter game where you control a player character (blue circle) using the left and right arrow keys (or on a smartphone, you can tap on the left or right side of the screen to move). The goal is to shoot down falling objects (red circles) by clicking on them.
Every time you successfully shoot a target, your score increases. If any of the targets hit the player, the game will end. The current score is displayed at the top left corner of the canvas.
Note: This code is just a minimal implementation to illustrate the game mechanics. You can enhance it further by adding levels, power-ups, animations, sound effects, and other features according to your requirements.