Sure, here's an example of a simple shooting game implemented as a single HTML file using JavaScript:
In this game, the player moves a blue rectangle using the arrow keys to shoot at red targets represented by other rectangles. The game ends when the player hits a target or the target reaches a certain point.
Please note that this is just a simple example and can be further expanded and improved. You can customize the graphics, add scoring, levels, and additional gameplay mechanics as per your requirements.