Honestly, I think it's really easy for developers to claim that they can do something like mobile-first UI, or using libraries like Formik and D3, but until you actually see a live version of their code, it's really hard to tell if it's the truth or not.
Making things even more complex is that their opinion of what it means to "know a library well" might differ vastly from yours.
Even having links to personal projects on Github that use said libraries or skills isn't sufficient proof, because unless you clone their library and run it locally, you can't even tell if it really works, or if it looks good.
At the end of the day, code is just code. Seeing a live version that is functioning properly is just as important as reading the source code.
For these reasons, I set up a Live Code Examples page which achieves a few different things. Firstly, it gives me a place to put up live examples of code I think is impressive or useful.
It also proves my aptitude in implementing certain libraries and techniques, and it also serves as a central repository for myself. So if I want to remember how to implement a dropdown using Formik and React Select, I can look it up easily and see a working version.
Please navigate through the menu to see my work.