Sure! Here's an example of a simple platformer game implemented in a single HTML file using JavaScript:
In this game, you control a red square (representing the player) using the left and right arrow keys to move horizontally, and the spacebar to jump. The player is affected by gravity and can only jump when on the ground, represented by the groundLevel variable. The player's position is updated based on its velocity, and the updatePlayer function is called repeatedly to simulate continuous movement.