React - How to export a pure stateless component

ES6 doesn't allow export default const. You must declare the constant first then export it:

const Header = () => {
  return <pre>Header</pre>
};
export default Header;

This constraint exists to avoid writting export default a, b, c; that is forbidden: only one variable can be exported as default

Just as a side note. You could technically export default without declaring a variable first.

export default () => (
  <pre>Header</pre>
)