The process is long, but they have a lot of flexibility for interviews, and I found it to be an enjoyable and interactive experience, even with the stress of being an interviewee. I didn't get an offer, but I learned, and I got good feedback from them.

1. HHRR call (I applied through a recruiter)
2. Introductory meeting with 2 engineers. They asked me about my expectations and work experience.
3. Hackerrank test (90 minutes). This was mostly about async JavaScript, basic CSS, consuming some data, and filtering. You don't need to have a perfect test to pass to the defense; mine wasn't.
4. Hackerrank defense: going through every Hackerrank answer. I was asked about error management (front-end and back-end responsibilities), some optimizations (why I was using map/filter/etc. or a for loop), and CSS.
5. Full technical interview: They asked me about pure JS like PropTypes, OOP, HTML, CSS, what is the last thing I learned and how I would explain it, and a real-case scenario about rendering/listing/etc. 6 & 7. Same-day 30' meetings: Adyen Formula Fit interview and Board interview with someone from the C-level. They say you will know the final decision on the same day of these interviews.

Challenge/Defense: async javascript, error management, basic CSS