Sure! Here's an example of a shooter game implemented as a single HTML file using JavaScript, enclosed in script tags:
In this game, you control a blue circle at the bottom of the canvas (representing the player) using arrow keys (left and right) on a computer or touch controls on a smartphone. Your aim is to shoot small black bullets at the red target by clicking anywhere on the canvas. Each time you hit the target, you earn coins. You can then use the coins to buy upgrades to increase the number of coins you earn per hit. The current number of coins and the upgrade cost are displayed on the screen. Additionally, an "Buy Upgrade" button is provided for smartphone operation.
Please note that this is a simplified implementation for demonstration purposes and can be further improved and enhanced based on your specific requirements.