I might be punished for this, but it has to be said. First, I agree that learning can be a challenging process and helping someone may make a difference between a drop and an accomplished person. But then, I wonder your friend finally comprehended or not the recursion when landed on that "damn good one" job of "js full stack programmer". If he still doesn't, chances are other important concepts eludes him too, and the pain of his limited understanding can be felt only by his fellow colleagues, not by you. His code may be clean (which I personally appreciate), but that is rarely enough by itself. What is or isn't acceptable needs to be judged by the task at hand, and as sympathetic as one may be, red lines must be drawn all the time (and that is what the article actually does). For average JS implementation tasks your friend may be OK, but you really wouldn't want to encourage him (just out of moral sense of fairness) to get into say, some life-critical systems development without the necessary competence.