html uses script tags to include code in the browser. that's it. outside of that was the "wild west" of js because, it wasn't supposed to run there. So, they did whatever they felt like. Then they couldn't agree and the "most popular" wins until the ecosystem argues with one another. it's a very dysfunctional "family". the only standard that came about was later, and that hasn't been 100% supported or implemented across the board yet, STILL.