I applied online and it was clear from my resume and the conversations that followed that I had not worked with React before. However in response to my application, I got a phone screen with the CTO, then a face to face interview with a CTO and Engineer, then I was given a coding test. I learned enough React to be able to finish their coding test in and submitted it. My application was not successful and the feedback I got was that I did not use some advanced React techniques. In summary, this was not a good experience, they want you to spend time learning something when other candidates with more specific experience in that tech have a clear advantage over you. Try elsewhere and do not waste your time here.