React Compiler

What Is the React Online Compiler?

The React Online Compiler lets you write JSX and CSS directly in your browser and see the results instantly. It uses Babel to transpile your JSX into standard JavaScript and renders your components with React 18. You get a split-pane editor with a JSX panel, a CSS panel, and a live preview iframe. React Hooks such as useState, useEffect, useRef, and useMemo are fully supported, so you can build interactive, stateful components without any local setup.

How It Works

1. Write your JSX component code in the left-hand editor panel.
2. Add any CSS styles in the CSS editor below the JSX panel.
3. Click the Run button in the header toolbar.
4. Babel standalone compiles your JSX into plain JavaScript in the browser.
5. React 18 and ReactDOM load via CDN inside a sandboxed iframe.
6. Your compiled component renders in the output preview on the right.

Step-by-Step Example

Follow these steps to create a simple counter component:

1. In the JSX editor, define a function component called App that uses React.useState(0) to track a count value.
2. Return a <div> containing an <h1> that displays the current count and a <button> with an onClick handler that increments the count.
3. In the CSS editor, add styles for your container, heading, and button to give the component a polished look.
4. Click Run to compile and render. The counter appears in the output panel, and clicking the button updates the count in real time.

Use Cases

• Learning React — Experiment with components, props, and state without installing Node.js or create-react-app.
• Prototyping components — Quickly build and iterate on UI components before adding them to a full project.
• Testing Hooks — Try out useState, useEffect, useRef, useMemo, and custom hooks in isolation.
• Sharing demos — Write a self-contained React example to share with colleagues or in tutorials.
• Teaching — Demonstrate React concepts in workshops, classrooms, or online courses with zero setup required.

Limitations & Notes

• No npm package installation is available. Only React and ReactDOM are loaded.
• File imports and module resolution are not supported. All code lives in a single JSX editor.
• React and ReactDOM are loaded via CDN (unpkg), so an internet connection is required.
• The compiler handles a single component file. Multi-file projects are not supported.
• React Router, Redux, and other third-party libraries cannot be used.
• API calls and fetch requests from the iframe may be blocked by CORS policies.
• All execution happens in the browser. There is no server-side rendering or Node.js runtime.

Sources & References

• React documentation — Official guides and API reference for React.
• React Hooks API — Reference for useState, useEffect, and all built-in hooks.
• Babel documentation — Learn how Babel compiles JSX and modern JavaScript.
• MDN JavaScript — Comprehensive JavaScript language reference.
• ReactDOM API — Reference for ReactDOM.createRoot and rendering methods.

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