Why ReactJS needs compilation

Question

Reactjs is consists of .js files and JavaScript doesn't compile as it's an interpreted language. Then why Reactjs need to be compiled? I read that it uses the JSX compiler.

Answer 1

JSX includes markup syntax that isn't valid javascript. The JSX "compiler" translates the markup into vanilla javascript. You can see this yourself using the babel repl:

JSX in:

const Test = () => <div>test</div>

Javascript out:

"use strict";

var Test = function Test() {
  return /*#__PURE__*/React.createElement("div", null, "test");
};

There's also the matter of bundling, resolving imports, adding polyfills, etc.