Sure, I can provide you with a basic outline of a simple 3D endless runner game implemented as a single HTML file using JavaScript. Please note that this is just a rough example and can be further enhanced and customized based on your requirements.
In this example, the game is played on a smartphone by using left and right arrow keys for movement. The player object is denoted by a red box, while the obstacles are green boxes. The player must dodge the obstacles by moving left or right and earn points for each successfully passed obstacle. The game ends if the player collides with an obstacle. The score is displayed on the screen, and once the game ends, an alert message shows the final score.