Sure! Here's a simple space shooter game implemented as a single HTML file using JavaScript. Please note that for a full-fledged game, additional functionalities and styling would be required, but this should give you a starting point.
Save the above code in a single HTML file, and you should have a basic space shooter game that can be played on a smartphone. The player can move the spaceship horizontally using touch controls, and shoot by tapping on the screen. Enemies will appear from the top, and the player needs to shoot them down before they reach the bottom. When a collision occurs, an explosion effect is shown.