My comment was more to indicate that the line in question is hard to evaluate as an objective "mistake", and I personally would not evaluate it as such.
If we ourselves don't know what's being stored, then it's a matter of concern. If used JS in the right way, it will help to do wonders. Else, get ready to fix bugs mate, lol. I had the same mindset during the early stage of my career. Way to go.
I have the same opinion as Brandin as a dev of 15 years. Also your way of communicating is quite patronising. In a language like JS, this kind of conditional makes sense, especially in bigger projects with multiple developers. It adds no weight but is a stricter check that helps to prevent bugs. If this value is changed by someone to a non-truthy value for whatever reason, a code review will most likely not catch it and even your tests might work and you have an extremely hard to track bug. Software projects are never perfect and you should never assume so.
In our company of 150+ devs, the strict checks in loosely typed languages are actually in the coding standards and will get flagged if you don't do them.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.