People have been using React since 2014. Is 3 years really still "du jour"?

Yes absolutely. Unfortunately in the javascript world it probably means that it's legacy by now.

Certainly, compared to something solid and well-understood like Javascript which has been around since 1997.

I'd complain the same way if it were a C++ project requiring Boost or something.

Boost has existed since 1999-2000, which aligns with ES3.

As for solid and well-understood... Douglas Crockford wrote a book on how "solid" Javascript is, called "Javascript: The Good Parts". One of his most common refrains about JS was "Javascript is The World's Most Misunderstood Programming Language". [0][1]

ES5 came out in 2009. ES6 was standardized after React came out.

[0] - http://javascript.crockford.com/javascript.html

[1] - http://javascript.crockford.com/popular.html

Yes, yes it is

It's about having a declarative UI library. React is just the syntax Facebook prefers.

Shall we do it in jQuery?