In my case, there wasn't really a job description beforehand. I had several conversations with Kevin and Sam through email and phone and I've interviewed there once before in 2015. My interview was more of a formality to see if I would vibe with the rest of the team.
I was asked my opinion on a few JavaScript frameworks, and if my experience with React and Redux. I told them I had a little bit of experience with React and none with Redux. However, I have worked with AngularJS, Ember, Sproutcore, KnockoutJS.
I was also told I would be mentoring some junior developers and that I would eventually be in charge of the front-end on their most legacy project.
Long story short, I got the job.