I don't think you'd really like to see any code like that in production. The point of an interview is to demonstrate your talents as they relate to the job. While fiddling with types is fun, it is not really relevant and is the exact opposite of what you should be doing in a real codebase. The person in this interview chose to do something silly to show off. They could have demonstrated their actual TS knowledge but instead they chose to write something totally unreadable after the interviewer asked them not to once, then made a specific rule which is basically telling them to drop the silly type stuff and just write normal code. If you really wanted the job, would you behave like that in the interview?