Sure! Here's a simplified implementation of the game "Slime Defense" as a single HTML file using JavaScript:
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This code sets up the basic structure of the game, including the game layout, variables for score, health, and gun power. The `updateUI` function is used to display the current game state on the screen. The `shoot` function handles shooting projectiles and updates the score and gun power accordingly.
The `upgradeGun` function allows the player to upgrade their gun based on their score. There are three choices: 1 for the laser gun, 2 for the purple skull gun, and 3 for the destroyer gun. The function deducts the score points needed and updates the gun power.
Finally, the `startGame` function initializes the game and calls the `updateUI` function to display the initial game state on the screen. The actual game logic for slime movement and interaction would need to be implemented separately.
Note: This is a simplified implementation and doesn't include the full game logic. You'll need to build upon this basic structure to make a fully functional game.