To prevent messages from being delivered before the destination is ready, client.postMessage() does not dispatch the message until one of the following has occurred on the destination: - 'DOMContentLoaded' event is fired. - onmessage is set. - startMessages() is called.



Specification link

Specification being incubated in a Community Group

Status in Chromium


Enabled by default (tracking bug)

Consensus & Standardization

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


Last updated on 2021-12-13