I believe Map was released in 2015 as part of ES6 so while not new, it still feels new in some code bases. Some people also confuse it with Array.prototype.map a lot.

People just assume every data structure operates like an array since it is the most commonly used without realizing the underlying object nature of the language. Like the idea of getters and setters coming from OOP paradigm is lost to fresh devs over the last 5 years using the FP paradigm as their primary means of coding in React.

So yeah some of the fundamental are missing but also most of the time this knowledge probably isn't utilized by React FP only devs in their day to day.