15 years ago, PHP didn't really support any programming paradigm very well, it was a huge untyped mess, the standard library was missing a lot of stuff, reusing code meant including individual files based on filesystem paths.

Today, PHP offers a solid OOP experience, good gradual typing, a larger and saner standard library and code loading based on namespaced components.

Now compare today's JS to PHP back in the day. It has the exact same kinds of problems. Except with modern JS, you'll end up adding TypeScript, webpack, Babel and a dozen other tools as well as several hundred megabytes of libraries to paper over all of those problems. But by doing that, you make the build process and the code that ultimately runs in a browser completely incomprehensible and undebuggable for the average developer. And then you start adding even more tooling (source maps that barely work) to try and solve that problem...

I had the impression that beside gradual typing, ES6 solved most of the mess (cleaner apis, modules) which was happening at the same time PHP (and python) accelerated their growth.

I find it really unfair to compare es6 to php 15 years ago, es6 is really cute (the babel/transpiling part is peculiar, I admit it)