Learning FP in JavaScript is part of learning JavaScript. In order to be productive on teams that use other techniques, you should definitely also learn how features like this, new, and class work. However, if you find the right team, you may also have the opportunity to help educate the rest of the team about the advantages of functional programming techniques, and how they work.

Many teams won’t be receptive to go all in on functional programming. However, many teams have already adopted React + Redux, and attempt to isolate side-effects from program logic.

Most teams will get it partially wrong — and that’s fine. That’s what code reviews and pair programming are for. You learn the right way to do things, and then share your knowledge openly with the rest of the team, and everybody wins.