Dec 19, 2025
3 min read
Google has updated their JavaScript SEO documentation with new canonical URL guidance for JavaScript-rendered pages.Keep canonicals consistent before and after rendering.
Google has updated its JavaScript SEO documentation with new guidance on handling canonical URLs for JavaScript-rendered sites.
The updated document also adds clear guidance to Google's best practices for including duplicate URLs.
An updated article focusing on time issues related to JavaScript sites: canonicalization can take twice as long as Google's processing time.
Google evaluates the canonical signal once when crawling the raw HTML for the first time, and then again after rendering the JavaScript.If your raw HTML contains a canonical URL and your JavaScript sets a different one, Google can receive conflicting signals.
The documentation states that injecting canonical tags via JavaScript is supported but not recommended.When JavaScript specifies a canonical URL, Google can retrieve it during rendering, but incorrect implementation can cause problems.
Changes to an existing canonical tag during rendering can lead to unexpected indexing results.
Related: What happens when Google chooses the wrong canonical URL?
Google recommends two best practices depending on how your website is structured.
The preferred method is to set the canonical URL in the raw HTML response to match the URL your JavaScript will eventually render.This gives Google consistent signals before and after rendering.
If JavaScript must set a different canonical URL, Google recommends leaving the canonical tag outside of the initial HTML.This can help avoid conflicting signals between the tracking and rendering phases.
The document also reminds developers to ensure that only one canonical tag exists on any given page after rendering.
See also: Google Announces Support for Cross-Domain Canonicals
Why is this important?
These guidelines cover details that can be easily missed when managing websites that display JavaScript.
The gap between the time Google crawls your HTML page and the time it renders your JavaScript creates opportunities for different special tags.
If you're using frameworks like React, Vue, or Angular that support client-side routing and page structure, it's worth checking how canonical tags are implemented.Check whether the server response contains the canonical tag and whether the JavaScript modifies or duplicates it.
In many cases, the solution is to coordinate your server-side and client-side canonical implementations so that they send the same signal to both phases of Google processing.
See also:Google shows you how to fix indexing problems caused by JavaScript
This documentation update explains behavior that may not have been seen before.It doesn't change the way Google handles primary tags.
If you see an unexpected canonical option in your Search Console page indexing data, check the mismatch between the raw HTML and the canonical tags.The URL review tool shows both raw and HTML, allowing you to compare the canonical usage in both levels.
Featured Image: Alicia97/Shutterstock
