Clarifications about the SharedArrayBuffer object message

Friday, March 19, 2021

Some of you might have received an email from Google Search Console with the subject "New requirements for SharedArrayBuffers". We received feedback that the message was confusing, and wanted to give some more insight into the issue, so that you can decide which next steps are appropriate. We also updated the guide on enabling cross-origin isolation to include additional details.

Why did I receive the message?

You received the message because we've detected that JavaScript on your website was using the SharedArrayBuffer object at the time of the message. The usage might be due to frameworks, libraries, or other third-party content included within your website.

What is the SharedArrayBuffer?

SharedArrayBuffer is a JavaScript object to share a memory space across threads on a website. It was used by websites before the vulnerability called Spectre was found. However, because Spectre was a CPU level vulnerability and it's unlikely to be fixed in the foreseeable future, browsers decided to disable the SharedArrayBuffer object.

While Chrome re-enabled it on desktop with Site Isolation as a temporary remedy, cross-origin isolation was standardized as a way to safely enable the SharedArrayBuffer object. Starting with version 91, planned to be released in late May 2021, Chrome will gate the SharedArrayBuffer object behind cross-origin isolation. Firefox enabled the SharedArrayBuffer object on a cross-origin isolated environment as well in version 76. We hope other browsers will follow soon.

Finding SharedArrayBuffer object usage on your site

You have two options:

  1. Use Chrome DevTools and inspect important pages.
  2. (Advanced) Use the Reporting API to send deprecation reports to a reporting endpoint.

Learn how to take the above approaches at Determine where the SharedArrayBuffer object is used on your website.

Next steps

For next steps, we recommend:

  1. Determine where the SharedArrayBuffer object is used on your website.
  2. Decide if the usage is necessary.
  3. Fix the issue by either removing the functionality, or by enabling cross-origin isolation.

If you haven't heard about the SharedArrayBuffer object, and you received a Search Console message about it, it's highly likely a third-party resource on your website is using it. Once you determine which pages are affected, and who the owner of the resource is, reach out to the resource provider and ask them to fix the issue.

After Chrome 91 is released, the SharedArrayBuffer object without cross-origin isolation will no longer be functional. In practice, this means that Chrome users on your site may experience degraded performance similar to other situations where the SharedArrayBuffer object is not supported.

We hope this clarification was useful, even if you didn't receive the message. If you have any questions, we'd recommend posting in the Search Central help community to get input from other experts.