A simple lightweight set of tools to work with DOM elements, create styles, and states to make it all dynamic.
When you're working on a small, maybe even medium project, it may be overkill to pull in something like React or Vue. Why add 2.99MB to a simple project that only utilizes 5% of Reacts features.
Of course there are others who made stuff like this before, for example Grecha.js. But I'd prefer to sacrifice just a little bit of that performance for convenience.