Below is an example of a simple rollercoaster platformer game implemented in a single HTML file using JavaScript and enclosed in script tags:
You can run the code by saving it to an HTML file and opening it in a web browser. The game is playable on a smartphone or desktop browser, and it utilizes touch-based controls for jumping. The player moves horizontally continuously and can jump to avoid falling off the platform. Adjust the provided constants (e.g., speed, gravity, jump height) to tweak the game behavior to your liking.