Sure! Here's an example of a simple platform game implemented as a single HTML file with JavaScript:
In this game, you control a red square (representing the player) using the up arrow key. The objective is to jump and land on a blue platform. The player can jump twice before reaching the ground. If the player falls off the screen, they are respawned at the top.
Please note that this is a minimal implementation to demonstrate the basic mechanics of a platform game. You can customize and expand upon it further to add more levels, enemies, or additional functionality as desired.