Sure! Here's an example of an idle game implemented in a single HTML file using JavaScript:
Idle Game
Score: 0
This simple idle game allows the player to click on an image to increase their score. They can use the score to purchase upgrades that increase their clicking power. The score and upgrade buttons are displayed on the page using `span` and `img` elements with appropriate ids. The initial clicking power is 1, and it increases by 1 with each upgrade. The cost of the next upgrade doubles each time the player makes an upgrade.