Honest questions: what's to stop that person from calling themselves a JavaScript developer? Why shouldn't he/she? What in the words "JavaScript Developer" impl

Honest questions: what's to stop that person from calling themselves a JavaScript developer? Why shouldn't he/she? What in the words "JavaScript Developer" imply professional ability? It's hard for me to imagine how this person learning a little jQuery, and calling themselves a developer, somehow saturates what master craftsmen of JS/jQuery do. 1) They won't be stealing contract jobs from the master craftsmen, as a quick look at each person's portfolio would reveal who the better developer is. 2) They won't be stealing full-time work from the master craftsmen, as the phone interviews and in-person would quickly whittle away the new developer.