Ask HN: JavaScript Framework to use with pre-existing HTML

I have a project that allows users to enter an arbitrary URL and make simple modifications to the HTML structure.

Right now I am doing this all by hand using ES6 but it's starting to get a bit unwieldy.

React, Vue.js, Angular etc are primarily focused on generating a complete project, HTML JS and CSS that can be used as an application.

I want to just add some functionality to existing arbitrary HTML, but I'd like to do it in a somewhat modern fashion (things like backbone are at least somewhat better suited to this, but way out of fashion).

It seems like Vue might be my best bet but I just wanted to see if anyone else had any suggestions.