RenderToString

renderToString is a function used in server-side rendering to render a user interface component tree to an HTML string. It allows a server to produce the initial markup that will be sent to the client, enabling faster time-to-interactive and improved SEO when applicable. In React, the common form is ReactDOMServer.renderToString, which takes a component tree and returns a string containing HTML markup that represents the rendered UI. The resulting HTML can include additional attributes and data markers that enable client-side hydration, where the client-side library attaches event handlers and reuses the server-rendered markup.

The function executes in a non-browser environment and should not depend on browser globals. Components used during rendering should avoid browser-specific code unless guarded by runtime checks. renderToString serializes the output and does not execute client-side scripts or attach event listeners; these are handled later during hydration or on the client.

RenderToString is typically contrasted with renderToStaticMarkup, which returns HTML without the framework-specific data attributes and is suitable for static content. For progressive rendering, some ecosystems provide streaming variants (for example, a pipeable render stream) to start sending HTML before the whole tree is ready.

Common considerations include ensuring proper escaping to prevent XSS, managing data that should not be exposed, and balancing SSR with client-side rendering for interactivity. See also: renderToStaticMarkup, renderToPipeableStream, hydration, server-side rendering.