JavaScript rendering
The execution of a page's client-side JavaScript by a search engine so that content and links generated at runtime become indexable.
Crawling IndexingSecond wave of indexingWeb Rendering Service
Render queue
The deferred queue in which Google executes a page's JavaScript with a headless Chromium instance after the raw HTML has already been crawled.
In full
Google crawls the raw HTML first, then queues the URL for rendering when resources allow. Rendering runs an evergreen Chromium build that executes JavaScript, applies CSS and produces the rendered DOM Google actually indexes. The delay between crawl and render is usually short but is not guaranteed, so content that exists only after client-side JavaScript can be indexed later than server-rendered content — and links discovered only in rendered HTML are discovered later too.
Example
A React product page ships an empty `<div id="root">` in the HTML; Google indexes the title from HTML immediately but the specifications table only after rendering.
Related terms
DOM (Document Object Model)
The in-memory tree representation of a document that the browser builds from HTML and mutates with JavaScript; the rendered DOM is what…
Server-side rendering
Generating a page's full HTML on the server for each request, so crawlers and users receive complete markup without executing JavaScript.
Prerendering
Generating and caching a fully rendered HTML snapshot of a JavaScript page at build time or on request, so crawlers receive complete markup.
Hydration
Attaching client-side JavaScript behaviour to server-rendered HTML so a static page becomes interactive.