JS is as old as java, but they're both talking about the build process of JS.

in the beginning, JS wasn't really transcoded/compiled. The first time i personally found out about that was sometime after 2010 with coffeescript, not sure if there were preceeding examples.

and your claim that people move around is really false. React has been the defacto standard for a pretty long time at this point.

yes, other UI libraries/frameworks exist, but reacts marketshare has been extremely dominant since it displaced jquery/ember etc