Javascript dependency in PHP library

I have a PHP library that depends on a Javascript repo (also my lib). In the PHP lib, I don't want a CDN url or a minified copy. The PHP lib uses a framework (also home-brewed) that will compile the JS files together along with all the resources on my site.

I don't want to change anything about the JS lib, aka I don't want to make a composer.json file. I'm aware git submodule exists, though I'm not sure how to use it and I've read that it's a thoroughly bad way to handle dependencies, and I'm guessing my submodules wouldn't get included through composer?

Are there any other ways to include a JS dependency in a PHP library? (aside from copy+pasting the files) (and/or tips to make submodule a good option)

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