The folks at Vercel and MERJ put together a super deep dive on how Google Search handles indexing JavaScript. They analyzed over 100,000 Googlebot fetches across various sites to test and validate Google's SEO capabilities. In short, Google Search handles JavaScript incredibly well, almost as well as normal web pages.
I 100% recommend reading through it, it not only goes through the history of Google Search and indexing JavaScript, it goes through a number of SEO JavaScript myths and debunks them in detail.
These are the four myths it goes through:
- Myth1 : Google can't render client-side JavaScript.
Reality: Google completely renders 100% of HTML pages, unless they would otherwise throw an error. - Myth 2: Google treats JavaScript pages differently.
Reality: Regardless of JavaScript complexity, Google successfully renders pages and discovers links. - Myth 3: Rendering queue and timing significantly impact SEO.
Reality: Most pages spend less than 20 seconds in the rendering queue. - Myth 4: JavaScript-heavy sites have slower page discovery.
Reality: Sitemaps eliminate any differences between discovery across rendering methods.
Here is the Google timeline of JavaScript rendering:
- Pre-2009: Limited JavaScript support
- 2009–2015: AJAX crawling scheme
- 2015–2018: Early JavaScript rendering
- 2018–present: Modern rendering capabilities
Martin Splitt from Google commented on this on LinkedIn saying, "It's hard to measure things like this and I'm sure there's inaccuracies (thanks to crawl demand, probably) but this matches what I'm seeing in our data and in practice and what is whispered here and there by those, who're managing CSR sites."
Gary Illyes from Google commented on this on LinkedIn saying, "Interesting read from Vercel and Giacomo Zecchini about Google's rendering capabilities. The TL;DR is that Google's rendering capabilities are great for the modern web. Really worth a read." He then does joke hate on JavaScript. He also added how detailed a study this was by saying, "it's ridiculous. who does even think about injecting beacons to test these things?! it makes me happy-angry there are still people like this around."
Go check out the study over here.
Forum discussion at LinkedIn.
