By Matt G. Southern
Publication Date: 2025-12-17 14:56:00
Google updated its JavaScript SEO documentation with new guidance on handling canonical URLs for JavaScript-rendered sites.
The documentation update also adds corresponding guidance to Google’s best practices for consolidating duplicate URLs.
What’s New
The updated documentation focuses on a timing issue specific to JavaScript sites: canonicalization can happen twice during Google’s processing.
Google evaluates canonical signals once when it first crawls the raw HTML, then again after rendering the JavaScript. If your raw HTML contains one canonical URL and your JavaScript sets a different one, Google may receive conflicting signals.
The documentation notes that injecting canonical tags via JavaScript is supported but not recommended. When JavaScript sets a canonical URL, Google can pick it up during rendering, but incorrect implementations can cause issues.
Multiple canonical tags, or changes to an existing canonical tag during rendering, can lead to unexpected indexing…