Because this project is already there, I started it in year 2000 when most of those technologies didn't exist. I would need to code everything again in JS, and

Because this project is already there, I started it in year 2000 when most of those technologies didn't exist. I would need to code everything again in JS, and we are talking about more than 150 KLOC. Plus libraries that might not be available in JS. And then I would have two separate versions to maintain. No way I'm going to do that, I'm not getting paid for this project and I don't have enough free time. With Java on the other hand, I had a desktop app and an applet sharing the vast majority of the codebase, only very specific parts of the code (a small part of the UI and I/O code) differ. This is what was allowing me to maintain the project and support both desktop and browser, until the applet paranoia growed out of proportion and browsers put applets in permanent quarantine. Of course, if I started this project now rather than in 2000, I would probably make different decisions regarding language and technologies used. Although it would still be a bit annoying not to be able to use Java. It's not my favorite language, but I definitely prefer it to JS by a mile.