It is not part of the standard. It is another framework. And, in fact, it is one of the most complex frameworks to maintain web applications. The main problem is that it requires a different DOM manipulation code for each kind of state transition that occurs in the program. Which, with time, translates into too many bugs to maintain it. That is the reason why Facebook created React in the first place: https://youtu.be/nYkdrAPrdcw?t=750