Google has updated its JavaScript SEO document with canonical guidance to clarify how canonical URLs are handled on pages rendered using JavaScript. The update explains how canonical signals are interpreted when they appear in the original HTML, when they are added through JavaScript, or when the two do not match.
This clarification is intended to reduce confusion around canonicalization in JavaScript and does not reflect a change in how Google processes canonical URLs. Instead, it provides clearer insight into how Google’s indexing of JavaScript pages works during different stages of crawling and rendering.
What Google Says About Canonical URLs
In the updated document, Google added the given section:
“The rel=”canonical” link tag helps Google find the canonical version of a page. You can use JavaScript to set the canonical URL, but keep in mind that you shouldn’t use JavaScript to change the canonical URL to something else than the URL you specified as the canonical URL in the original HTML. The best way to set the canonical URL is to use HTML, but if you have to use JavaScript, make sure that you always set the canonical URL to the same value as the original HTML. If you can’t set the canonical URL in the HTML, then you can use JavaScript to set the canonical URL and leave it out of the original HTML.”
SEO Best Practices for JavaScript-Driven Websites
Based on site architecture, Google recommends the following canonical URL best practices:
- Set the canonical URL in the original HTML response and ensure it matches the canonical URL that JavaScript will render later. This provides consistent canonical signals during both the initial crawl and the rendering phase.
- If the canonical URL must be set using JavaScript, leave the canonical tag out of the original HTML entirely and ensure that JavaScript sets only one canonical value after rendering.
Following these practices helps prevent conflicting canonical signals between raw HTML and rendered content, reducing the risk of unexpected indexing behavior on JavaScript-rendered pages.
Key Takeaway
This documentation update clarifies how Google interprets canonical signals at different stages of crawling and rendering on JavaScript-driven pages. By outlining when canonical URLs are evaluated and how mismatches between HTML and JavaScript can affect indexing, Google aims to reduce confusion for site owners managing dynamic websites. Businesses managing JavaScript-rendered websites can benefit from working with a professional search engine optimization company to keep canonical signals consistent and avoid indexing issues.
