How Does React Tell a Class from a Function? (via) Understanding the answer requires a deep understanding of the history of the JavaScript class system plus how Babel and other tools work with it. “For an API to be simple to use, you often need to consider the language semantics (possibly, for several languages, including future directions), runtime performance, ergonomics with and without compile-time steps, the state of the ecosystem and packaging solutions, early warnings, and many other things. The end result might not always be the most elegant, but it must be practical.”