How Can I Structure My HTML5 Game for Multiple Levels with Different Mechanics?

I suggest looking into Vite as a development setup. It can help you bundle your JavaScript modules and manage dependencies using npm. It's a good expenditure of time while still sticking to plain JavaScript for your game logic!

A great way to organize your code and prepare for more levels is to split your game into multiple JavaScript classes across different files. You can import these classes into your main HTML file in the right order. Just make sure that each file's functions and variables are scoped appropriately to allow them to interact with one another. For example, have separate files for the game engine, levels, game objects, and so on! This approach keeps your code neat and makes it easier to manage different mechanics as your game grows.

If your game is not utilizing canvas and just relying on the DOM, then the approach might differ. You could use a component system to manage different game objects, or if you're going all-in with JavaScript, consider using frameworks like Phaser.js. They're designed to handle game mechanics smoothly.

Using `type="module"` in your script tag will let you utilize JavaScript modules! This way, you can `import` functions and classes you export from other modules. It's a powerful way to encapsulate different functionality and make your game easier to manage. Just keep in mind that for modules to work, you typically need to run a local server.