Recently for a job I was applying for I build a time tracking demo in React.
I've spent the last 4-5 years working with Angular (via Ionic) but many of the jobs I've seen are asking for React.
It's been easy to pick up and a lot of fun to work with. I like having this app as a demo because as I learn new things I'm able to include them in the app.
For instance, I'm very fond of SCSS for writing my styles. Variables and mixins are nice, but I love nested styles. I found a package react-app-rewire-css-modules which supports SCSS. It allows me to include a stylesheet for each of my components (as a CSS Module).
I've also figured out Redux. I was expecting it to be more difficult, but once I had the pieces in place it's actually pretty easy. I may run into issues with sharing data across reducers, but I'll cross that bridge when I get there.
If you'd like to follow along with my development here's the code: Time Tracking Demo.
If you're a React guru and would like to review my code and give me notes I'd appreciate it.