renderToStringLink for this heading

January 6, 2025 · View on GitHub

Pitfall

renderToString does not support streaming or waiting for data. See the alternatives.

renderToString renders a React tree to an HTML string.

const html = renderToString(reactNode, options?)

Reference
- renderToString(reactNode, options?)
Usage
- Rendering a React tree as HTML to a string
Alternatives
Troubleshooting
- When a component suspends, the HTML always contains a fallback

Reference Link for Reference

`renderToString(reactNode, options?)`Link for this heading

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

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

const html = renderToString(<App />);

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

See more examples below.

Parameters Link for Parameters

reactNode: A React node you want to render to HTML. For example, a JSX node like <App />.
optional options: An object for server render.
- optional identifierPrefix: A string prefix React uses for IDs generated by useId. Useful to avoid conflicts when using multiple roots on the same page. Must be the same prefix as passed to hydrateRoot.

Caveats Link for 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 Link for Usage

Rendering a React tree as HTML to a string Link for 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.

Pitfall

renderToString does not support streaming or waiting for data. See the alternatives.

Alternatives Link for Alternatives

Migrating from `renderToString` to a streaming render on the server Link for this heading

renderToString returns a string immediately, so it does not support streaming content as it loads.

When possible, we recommend using 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.

Migrating from `renderToString` to a static prerender on the server Link for this heading

renderToString returns a string immediately, so it does not support waiting for data to load for static HTML generation.

We recommend using these fully-featured alternatives:

If you use Node.js, use prerenderToNodeStream.
If you use Deno or a modern edge runtime with Web Streams, use prerender.

You can continue using renderToString if your static site generation environment does not support streams.

Removing `renderToString` from the client code Link for this heading

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 Link for Troubleshooting

When a component suspends, the HTML always contains a fallback Link for 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. For server side rendering, they can stream content in chunks as it resolves on the server so that the user sees the page being progressively filled in before the client code loads. For static site generation, they can wait for all the content to resolve before generating the static HTML.

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