javascript - JSX can be used without importing React

Question

I'm trying to run my first React JSX file with create-react-app with version 4.0.0 and it works! However, I don't have the import statements of React included in my JSX and it works too but it is very weird. The project is created by create-react-app command with version 4.0.0.

The App.js file:

/* without import React but works too! */

 import { Component } from "react";
class App extends Component {
  render() {
    return <div>456</div>;
  }
}
export default App;

Answer 1

Starting from React 17 it's not necessary to import React to use JSX. See from the blog post about that in the section called Removing Unused React Imports:

Because the new JSX transform will automatically import the necessary react/jsx-runtime functions, React will no longer need to be in scope when you use JSX. This might lead to unused React imports in your code.

What’s a JSX Transform?

Browsers don’t understand JSX out of the box, so most React users rely on a compiler like Babel or TypeScript to transform JSX code into regular JavaScript.

Suggested read is Introducing the New JSX Transform. Also you can see Using React 17 and the new JSX transform with Create React App 4.0 Alpha.