JSX is stricter than HTML:

One root: a component returns a single element. Group siblings in a Fragment, <>…</>, when you do not want an extra <div>.
Close every tag: <img />, <br />, <input />.
camelCase attributes: className, htmlFor, onClick, tabIndex. Only aria-* and data-* keep their dashes.
Braces switch to JavaScript: any expression works ({score * 2}, {user.name}), but statements such as if and for do not. Comments go in braces too: {/* note */}.
style takes an object: style={{ color: 'gold' }}. The outer braces mean JavaScript; the inner ones are the object.

Markup inside JavaScript