Allows developers to selectively enable and disable use of synchronous script execution through the feature policy HTTP header or the <iframe> "allow" attribute. The identifier for the feature in policies is "sync-script". By default, synchronous script execution is allowed in all frames. If developers wish to disable this on any page, they can include a header like: Feature-Policy: sync-script 'none'


Status in Chromium


In development (tracking bug)

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

  • No signal
  • No signal
  • No signals


Last updated on 2022-01-21