Is Having 15 JavaScript Files on One Page Crazy or Common?

It's not really about the number of JS files but more about the complexity of what's being run. Lots of single-page apps use one HTML page and manage everything through JavaScript. That said, having 15 separate files will definitely slow things down compared to one. Each file adds latency due to network round-trips, especially if there are dependencies between them. If you're on a fast local network, it might not be an issue, but over the internet, it can be significant. Use your browser's dev tools to analyze what’s taking time and maybe even simulate slower connections. Remember, even if all files work, too many files can add unnecessary bandwidth and CPU costs.

In my experience, most production-level web apps tend to bundle JS files into one. However, if this is mostly custom code and you don't expect it to grow much more, keeping it all in a single file might be simpler. If you're using code from third-party libraries or expect the codebase to expand, then looking into bundlers like Webpack or Rollup could be a smart move. Generally, try to avoid adding complexity unless you really need it. Bundling can improve performance since it reduces the number of requests made by the browser, but there’s a trade-off with caching separate files.

The industry standard is to utilize tools like Vite as a development server because it conveniently bundles all the assets per page. If that seems like overkill for you, just sticking with JavaScript modules can work great too!