Sure, here's an example of a simple math shooting game implemented as a single HTML file with JavaScript:
In this game, your goal is to shoot the target by clicking on the canvas. The target will have a random math problem inside. If you hit the target with the correct answer, you earn points. The score is displayed on the top left corner of the canvas. The game will continue until you close the browser tab.
Note: This is a basic example and can be further enhanced with more features and graphics.