Sure! Here's a simple implementation of a 2D side-scrolling platformer game using HTML and JavaScript. You can try it out and play as a finished game:
To play the game, open the HTML file in your web browser on a smartphone or a web browser with a mobile view. Use the left and right arrow buttons on the on-screen keyboard to move the player left and right. Use the up arrow button to jump. The player (red ball) starts on a blue platform, and you need to jump on all the blue platforms while avoiding falling off the screen. When colliding with a platform from below, you will go through it, but if you collide from the top or side, it becomes solid.