JavaScript is often touted as one of the more complex topics in SEO. Its dynamic nature, while enabling modern user experiences, can also create visibility barriers for crawlers that struggle to process and render it correctly.

As search and discovery evolve toward AI-driven systems, ensuring that JavaScript websites remain fully accessible to both traditional and AI-based crawlers has become more important than ever.

This guide explores how search engines like Google render JavaScript, what happens when crawlers cannot access rendered content, how AI systems handle JavaScript-based pages, and what methods developers can use to improve rendering accessibility.

How Google renders websites when crawling

Google’s crawling and indexing process follows four main stages: Crawl, Render, Index, and Rank.

  1. Crawl – Googlebot discovers and fetches URLs from sitemaps, internal links, and external sources.
  2. Render – When JavaScript is detected, the page is passed to Google’s Web Rendering Service (WRS). This system uses a headless version of Chrome to process and execute JavaScript, building a Document Object Model (DOM) similar to what a user would see in their browser.
  3. Index – The rendered content, links, and metadata are then stored in Google’s index.
  4. Rank – Google applies ranking algorithms based on the content, context, and relevance of the page.

Because rendering JavaScript is computationally expensive, Google often performs a secondary rendering step.

The initial crawl may index basic HTML content, while the secondary rendering fetches JavaScript-dependent elements once resources allow. Google also employs a rendering cache to avoid reprocessing scripts across multiple sites that use common frameworks like React, Vue, or Angular.

What happens if a crawler cannot render JavaScript?

If a crawler cannot render or execute your JavaScript correctly, critical content or links may remain hidden, leading to incomplete or missing indexing.

There is an important distinction between:

  • DOM Response: The HTML source code that a crawler receives before JavaScript executes.
  • Browser Render: The fully constructed DOM after JavaScript execution, including dynamically injected content.

If your site relies heavily on client-side rendering, the DOM response might be empty or minimal. Crawlers that don’t execute JavaScript will see an incomplete version of the page. This can result in missing titles, body text, structured data, or internal links in the indexed version.

Can AI Crawlers Render JavaScript?

Unlike Googlebot, most AI crawlers do not yet render JavaScript. According to OpenAI’s documentation, ChatGPT’s browsing tool uses a simplified text extraction process rather than full DOM rendering.

Similarly, Perplexity’s help documentation confirms it retrieves HTML snapshots and does not execute JavaScript.

Anthropic’s Claude also focuses on text-based parsing rather than rendering dynamic content.

This means that live crawls by AI systems are limited to what is present in the static HTML response. Any content loaded dynamically via JavaScript may be invisible to them.

This also correlates with the information shared by Andrej Kaparthy, in that when the LLMs receive training data, e.g., webpages, they initially strip the pages of all CSS, JS, etc, until there is just the text left. They then pass this onto processing to be trained on.

Could Comet and Atlas Improve JavaScript Rendering in AI Crawlers?

OpenAI’s Comet browser (used by ChatGPT) and Perplexity’s Atlas browser aim to improve the efficiency and fidelity of web previews.

Early indications suggest these systems may include rendering capabilities that better approximate what a human user sees. If these browsers begin to support cached or partial rendering of JavaScript-based pages, AI crawlers could start interpreting modern frameworks more accurately.

While details remain limited, these technologies may introduce a middle ground between raw HTML scraping and full headless rendering, using cached or pre-processed renders for popular sites.

Common Methods to Resolve JavaScript Rendering Issues

Server-Side Rendering (SSR)

SSR executes JavaScript on the server and delivers a fully rendered HTML page to the client. Frameworks like Next.js or Nuxt.js support SSR by default. This approach ensures that both users and crawlers receive the same complete content without relying on client-side execution.

Static Pre-Rendering

Also known as pre-rendering or static site generation (SSG), this technique builds fully rendered HTML files during deployment. It’s ideal for sites with predictable content, allowing crawlers to access static snapshots while users still benefit from dynamic interactivity.

Hydration

Hydration bridges SSR and client-side rendering. The initial page is pre-rendered on the server, then JavaScript “hydrates” it in the browser to enable interactivity. This hybrid approach provides SEO-friendly output while maintaining dynamic features.

Compressed Plain Text Views for Specific User Agents

Some developers create simplified, text-only versions of pages for crawlers that cannot execute JavaScript. This can be done via user-agent detection and is often used for headless bots like Facebook’s crawler or AI-based scrapers. While effective, it should be implemented carefully to avoid cloaking.

Conclusion

JavaScript websites don’t have to be SEO black boxes. By understanding how crawlers process your site and implementing rendering-friendly architectures, you can ensure that both search engines and AI systems access your full content.

As AI-driven discovery expands, websites that blend technical SEO precision with render-efficient delivery will gain the upper hand. If your site depends heavily on JavaScript, now is the time to audit its renderability and ensure it’s both search and AI crawler friendly.

Need help optimising your JavaScript site for search and AI discovery? Get in touch to run a JavaScript SEO visibility audit and uncover what your site is truly showing to both Googlebot and the next generation of AI crawlers.