renderToString

const html = renderToString(reactNode)

• Reference
  • renderToString(reactNode)
• Usage
  • Rendering a React tree as HTML to a string
• Alternatives
  • Migrating from renderToString to a streaming method on the server
  • Removing renderToString from the client code
• Troubleshooting
  • When a component suspends, the HTML always contains a fallback

Reference

renderToString(reactNode)

On the server, call renderToString to render your app to HTML.

const html = renderToString(<App />);

On the client, call hydrateRoot to make the server-generated HTML interactive.

Parameters

• reactNode: A React node you want to render to HTML. For example, a JSX node like <App />.

Returns

An HTML string.

Caveats

• renderToString has limited Suspense support. If a component suspends, renderToString immediately sends its fallback as HTML.

• renderToString works in the browser, but using it in the client code is not recommended.

Usage

Rendering a React tree as HTML to a string

Call renderToString to render your app to an HTML string which you can send with your server response:

import { renderToString } from 'react-dom/server';

// The route handler syntax depends on your backend framework
app.use('/', (request, response) => {
  const html = renderToString(<App />);
  response.send(html);
});

This will produce the initial non-interactive HTML output of your React components. On the client, you will need to call hydrateRoot to hydrate that server-generated HTML and make it interactive.

Alternatives

Migrating from renderToString to a streaming method on the server

renderToString returns a string immediately, so it does not support streaming or waiting for data.

When possible, we recommend to use these fully-featured alternatives:

• If you use Node.js, use renderToPipeableStream.
• If you use Deno or a modern edge runtime with Web Streams, use renderToReadableStream.

You can continue using renderToString if your server environment does not support streams.

Removing renderToString from the client code

Sometimes, renderToString is used on the client to convert some component to HTML.

// 🚩 Unnecessary: using renderToString on the client
import { renderToString } from 'react-dom/server';

const html = renderToString(<MyIcon />);
console.log(html); // For example, "<svg>...</svg>"

Importing react-dom/server on the client unnecessarily increases your bundle size and should be avoided. If you need to render some component to HTML in the browser, use createRoot and read HTML from the DOM:

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

const div = document.createElement('div');
const root = createRoot(div);
flushSync(() => {
  root.render(<MyIcon />);
});
console.log(div.innerHTML); // For example, "<svg>...</svg>"

The flushSync call is necessary so that the DOM is updated before reading its innerHTML property.

Troubleshooting

When a component suspends, the HTML always contains a fallback

renderToString does not fully support Suspense.

If some component suspends (for example, because it’s defined with lazy or fetches data), renderToString will not wait for its content to resolve. Instead, renderToString will find the closest <Suspense> boundary above it and render its fallback prop in the HTML. The content will not appear until the client code loads.

To solve this, use one of the recommended streaming solutions. They can stream content in chunks as it resolves on the server so that the user sees the page being progressively filled in even before the client code loads.