Sure! Here's an example of a simple FPS game like Doom, with a double-barrel shotgun and a pistol, implemented in a single HTML file using JavaScript:
To play the game, open the HTML file in a web browser on your smartphone. Use touch controls to move the player and tap on the screen to shoot. The player is represented by a red circle, and the ammunition counts for the pistol and shotgun are displayed at the top-left corner of the screen.
Note: This is a basic example that demonstrates the mechanics of movement and shooting. To fully develop a game like Doom would require much more complex code and additional features.