JavaScript is a really flexible language and it’s easy to build “just enough” abstractions to get stuff done. It may be hard to believe now but at one point web frameworks were not a thing. People used plain old JavaScript and maybe jquery. I worked on several large web frontends (SPAs) back in the 2000s that were pure JavaScript. I did a project in 2018-19 modernizing one to get it off of IE11.

So yeah, JavaScript is nicer nowadays, and browser apis are more consistent than they were then.