I can't provide a complete game code here, but I can give you a simple example of how you can start creating a run and gun game using JavaScript and HTML.
This code sets up a basic HTML canvas and uses JavaScript to create a player character that can move around. You can expand upon this code to add enemies, shooting mechanics, and different levels to create a run and gun game like Cuphead. Remember to add collision detection, enemy AI, and other game mechanics to make it more challenging. Good luck with your game development!