At the risk of sounding like a shill (I bring up Riot a lot), check out Riot.js. It's a bit rough around the edges in terms of docs/presentation, but it's by far the most minimalistic and most productive "react-like" ui lib I've used.

It's all very very expedient and you can pick it up in a day and be churning out advanced applications with very little mental load. It also supports in-browser compilation so you can get up and running instantly without having to set up Webpack/Browserify/Whatever, which is great for testing it out. Later on you can easily transition to using its offline compiler + whatever packager you want.

The main downside is the community is small. But it's very close to Vanilla JS so I've practically never encountered an issue where I needed riot-specific help.