What is JavaScript SEO?
JavaScript SEO is the practice of making JavaScript-rendered content crawlable, renderable, and indexable. Modern frameworks (React, Vue, Angular, Next.js) often render content in the browser rather than in the initial HTML response, which forces search engines to execute JavaScript before they can see the page at all.
How Google renders JavaScript
Google renders JavaScript in a second wave: pages are crawled, queued for rendering in headless Chromium, and only then fully indexed. This adds delay and failure modes. Content that appears only after a click, depends on failed API calls, or renders behind client-side errors may never be indexed. Most other crawlers, and many AI crawlers, execute little or no JavaScript at all.
The reliable fix is server-side rendering or static generation, where complete HTML ships in the initial response. The diagnostic workflow: compare the raw HTML response against the rendered DOM, inspect the page with the URL Inspection tool in Search Console, and crawl the site with JavaScript rendering toggled on and off to find content that exists only client-side.
Example
Example
A React single-page app loads product descriptions through a client-side API call. Googlebot indexes the pages with empty description areas because the call fails in the rendering queue. Moving the fetch to the server makes the full HTML visible to every crawler on first request.
Frequently asked questions
Can Google index JavaScript-rendered content?
Yes, but with delay and failure modes: rendering happens in a second wave and depends on scripts executing cleanly. AI crawlers like GPTBot mostly do not render JavaScript, so client-side-only content is invisible to them.
What is the difference between SSR and CSR for SEO?
Server-side rendering ships complete HTML in the first response, so every crawler sees the content immediately. Client-side rendering ships an empty shell plus scripts, making indexing dependent on successful JavaScript execution.