Sure! Here's an example of a simple platformer game implemented as a single HTML file using JavaScript and enclosed in script tags:
This example creates a simple platformer game where the player, represented by a blue square, can move left and right using the arrow keys. They can also jump by pressing the up arrow key. Gravity is applied to the player, making it fall back to the ground after jumping. The game loop ensures that gravity is constantly applied.
Note: This is a very basic example to demonstrate the implementation. To create a fully-featured platformer game, you would need to add more functionalities like collision detection, platforms, enemies, and scoring system.