createRoot

Creates a React root for rendering React components into a DOM container with concurrent rendering features.

import { createRoot } from 'react-dom/client';

const root = createRoot(container, options);

Reference

`createRoot(container, options?)`

Call createRoot to create a React root for displaying content inside a browser DOM element.

/src/client/ReactDOMRoot.js:171-260

const root = createRoot(document.getElementById('root'));
root.render(<App />);

Parameters

container

Element | Document | DocumentFragment

required

A DOM element, Document, or DocumentFragment that will contain your React app. React will create a root for this container and manage the DOM inside it.Validation:

Must be a valid DOM container
Cannot be a text node or comment node (unless feature flag enabled)
Should not be already managed by another React root

options

CreateRootOptions

Optional configuration object for the root.

Show options properties

onRecoverableError

(error: Error, errorInfo: ErrorInfo) => void

Called when React automatically recovers from errors. Useful for logging errors to an error reporting service.

createRoot(container, {
  onRecoverableError: (error, errorInfo) => {
    console.error('Recoverable error:', error);
    console.log('Component stack:', errorInfo.componentStack);
  }
});

The errorInfo object contains:

componentStack?: string - Stack trace of component hierarchy

onUncaughtError

(error: Error, errorInfo: ErrorInfo) => void

Called when an error is thrown and not caught by any error boundary.

createRoot(container, {
  onUncaughtError: (error, errorInfo) => {
    logErrorToService(error, errorInfo.componentStack);
  }
});

onCaughtError

(error: Error, errorInfo: ErrorInfo) => void

Called when an error boundary catches an error. The errorInfo includes the errorBoundary component reference.

createRoot(container, {
  onCaughtError: (error, errorInfo) => {
    console.log('Caught by:', errorInfo.errorBoundary);
  }
});

identifierPrefix

string

String prefix for IDs generated by useId. Useful to avoid conflicts when using multiple roots on the same page.

const root1 = createRoot(container1, { identifierPrefix: 'app1-' });
const root2 = createRoot(container2, { identifierPrefix: 'app2-' });

unstable_strictMode

boolean

Enable Strict Mode for this root. Helps identify potential problems by running effects twice in development.

createRoot(container, {
  unstable_strictMode: true
});

This is an unstable API. Use <StrictMode> component instead for better compatibility.

unstable_transitionCallbacks

TransitionTracingCallbacks

Callbacks for transition tracing. Experimental API for tracking concurrent transitions.

onDefaultTransitionIndicator

() => void | (() => void)

Called when a transition indicator should be shown. Can return a cleanup function.

Returns

root

RootType

A root object with two methods: render and unmount.

`root.render(reactNode)`

Renders a React component into the root’s DOM container.

/src/client/ReactDOMRoot.js:107-136

root.render(<App />);

Parameters

reactNode

ReactNode

required

A React node to render. Usually JSX like <App />, but can also be a React element created with createElement(), a string, a number, null, or undefined.

Notes

The first call replaces any existing HTML inside the container
Subsequent calls use React’s diffing algorithm to update efficiently
Does not support callback argument (removed in React 18)
Updates are batched and may be asynchronous

`root.unmount()`

Destroys a rendered React component and cleans up its DOM and event handlers.

/src/client/ReactDOMRoot.js:139-169

root.unmount();

Notes

Runs cleanup functions in useEffect and useLayoutEffect
Synchronously completes unmounting before returning
Should not be called while React is already rendering
Container is emptied but not removed from the DOM

Usage Examples

Basic Client Rendering

import { createRoot } from 'react-dom/client';
import App from './App';

const container = document.getElementById('root');
const root = createRoot(container);
root.render(<App />);

With Error Handling

import { createRoot } from 'react-dom/client';
import * as Sentry from '@sentry/react';

const root = createRoot(document.getElementById('root'), {
  onRecoverableError: (error, errorInfo) => {
    // Log recoverable errors (hydration mismatches, etc.)
    console.warn('Recoverable error:', error);
    Sentry.captureException(error, {
      contexts: {
        react: {
          componentStack: errorInfo.componentStack,
        },
      },
    });
  },
  onUncaughtError: (error, errorInfo) => {
    // Log uncaught errors
    Sentry.captureException(error, {
      contexts: {
        react: {
          componentStack: errorInfo.componentStack,
        },
      },
    });
  },
  onCaughtError: (error, errorInfo) => {
    // Log errors caught by error boundaries
    console.log('Caught by error boundary:', errorInfo.errorBoundary);
  },
});

root.render(<App />);

Multiple Roots on Same Page

import { createRoot } from 'react-dom/client';

// Create separate roots with unique ID prefixes
const headerRoot = createRoot(document.getElementById('header'), {
  identifierPrefix: 'header-',
});

const sidebarRoot = createRoot(document.getElementById('sidebar'), {
  identifierPrefix: 'sidebar-',
});

const mainRoot = createRoot(document.getElementById('main'), {
  identifierPrefix: 'main-',
});

headerRoot.render(<Header />);
sidebarRoot.render(<Sidebar />);
mainRoot.render(<MainContent />);

Updating the Root

import { createRoot } from 'react-dom/client';
import { useState } from 'react';

const root = createRoot(document.getElementById('root'));

// Initial render
root.render(<App initialCount={0} />);

// Later update - React will diff and update efficiently
setTimeout(() => {
  root.render(<App initialCount={5} />);
}, 1000);

Cleaning Up

import { createRoot } from 'react-dom/client';

const root = createRoot(document.getElementById('root'));
root.render(<App />);

// Clean up when done (e.g., in SPA navigation)
function cleanup() {
  root.unmount();
  // Container is now empty and ready for reuse
}

// Call cleanup when navigating away or app unmounts
window.addEventListener('beforeunload', cleanup);

TypeScript

import { createRoot, type Root } from 'react-dom/client';

interface CreateRootOptions {
  unstable_strictMode?: boolean;
  unstable_transitionCallbacks?: TransitionTracingCallbacks;
  identifierPrefix?: string;
  onUncaughtError?: (
    error: unknown,
    errorInfo: { componentStack?: string }
  ) => void;
  onCaughtError?: (
    error: unknown,
    errorInfo: {
      componentStack?: string;
      errorBoundary?: React.Component;
    }
  ) => void;
  onRecoverableError?: (
    error: unknown,
    errorInfo: { componentStack?: string }
  ) => void;
  onDefaultTransitionIndicator?: () => void | (() => void);
}

const container = document.getElementById('root');
if (!container) throw new Error('Root container not found');

const root: Root = createRoot(container, {
  onRecoverableError: (error, errorInfo) => {
    console.error('Recoverable error:', error);
  },
});

root.render(<App />);

Migration from React 17

Before (React 17)

import ReactDOM from 'react-dom';

ReactDOM.render(
  <App />,
  document.getElementById('root'),
  () => {
    console.log('Rendered!');
  }
);

// Unmounting
ReactDOM.unmountComponentAtNode(document.getElementById('root'));

After (React 18+)

import { createRoot } from 'react-dom/client';
import { useEffect } from 'react';

const root = createRoot(document.getElementById('root'));

// Move callbacks into component
function App() {
  useEffect(() => {
    console.log('Rendered!');
  }, []);
  
  return <div>...</div>;
}

root.render(<App />);

// Unmounting
root.unmount();

Common Pitfalls

Don’t call render in render

// Bad: Causes infinite loop
function App() {
  root.render(<App />); // Don't do this!
  return <div>App</div>;
}

// Good: Use state to trigger updates
function App() {
  const [count, setCount] = useState(0);
  return <button onClick={() => setCount(count + 1)}>{count}</button>;
}

Don’t create multiple roots for same container

// Bad: Creating multiple roots for same element
const root1 = createRoot(container);
const root2 = createRoot(container); // Error!

// Good: Reuse the same root
const root = createRoot(container);
root.render(<App1 />);
root.render(<App2 />); // This is fine - updates the same root

Don’t forget to handle errors

// Bad: Errors crash the app silently
const root = createRoot(container);
root.render(<App />);

// Good: Handle errors gracefully
const root = createRoot(container, {
  onRecoverableError: (error) => {
    logToService(error);
  },
});

root.render(
  <ErrorBoundary>
    <App />
  </ErrorBoundary>
);

Browser Compatibility

createRoot requires:

Modern browsers (Chrome 90+, Firefox 88+, Safari 14.1+, Edge 90+)
ES6 features: Map, Set, Promise
DOM features: Element, Document, DocumentFragment

For older browsers, include polyfills:

<script src="https://unpkg.com/core-js-bundle@3/minified.js"></script>

Performance Considerations

Concurrent rendering - createRoot enables concurrent features like transitions and Suspense
Automatic batching - Multiple state updates are batched automatically
Interruptible rendering - React can pause and resume rendering work
Smooth updates - Long-running updates don’t block user interactions

hydrateRoot - For hydrating server-rendered content
flushSync - Force synchronous updates
createPortal - Render children into different DOM node

React Core

Hooks

ReactDOM

Server APIs

createRoot

createRoot

Reference

`createRoot(container, options?)`

Parameters

Returns

`root.render(reactNode)`

Parameters

Notes

`root.unmount()`

Notes

Usage Examples

Basic Client Rendering

With Error Handling

Multiple Roots on Same Page

Updating the Root

Cleaning Up

TypeScript

Migration from React 17

Before (React 17)

After (React 18+)

Common Pitfalls

Don’t call render in render

Don’t create multiple roots for same container

Don’t forget to handle errors

Browser Compatibility

Performance Considerations

React Core

Hooks

ReactDOM

Server APIs

​createRoot

​Reference

​createRoot(container, options?)

​Parameters

​Returns

​root.render(reactNode)

​Parameters

​Notes

​root.unmount()

​Notes

​Usage Examples

​Basic Client Rendering

​With Error Handling

​Multiple Roots on Same Page

​Updating the Root

​Cleaning Up

​TypeScript

​Migration from React 17

​Before (React 17)

​After (React 18+)

​Common Pitfalls

​Don’t call render in render

​Don’t create multiple roots for same container

​Don’t forget to handle errors

​Browser Compatibility

​Performance Considerations

​Related APIs

createRoot

Reference

`createRoot(container, options?)`

Parameters

Returns

`root.render(reactNode)`

Parameters

Notes

`root.unmount()`

Notes

Usage Examples

Basic Client Rendering

With Error Handling

Multiple Roots on Same Page

Updating the Root

Cleaning Up

TypeScript

Migration from React 17

Before (React 17)

After (React 18+)

Common Pitfalls

Don’t call render in render

Don’t create multiple roots for same container

Don’t forget to handle errors

Browser Compatibility

Performance Considerations

Related APIs