Sure, here's an example of a simple game using JavaScript that can be implemented as a single HTML file and played on a smartphone. It uses pictograms to represent objects in the game.
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In this game, the goal is to tap the pictograms that appear in the game container as quickly as possible before the time runs out. Each correctly tapped pictogram will increase the score by 1. The game will end after 10 seconds and display the final score.