Primary eng (and PM) emails
Deprecate and retire window.postMessage(message, transferables,
targetOrigin) legacy overload.
A legacy overload of window.postMessage() that's nearly unused & it
would be preferable to finally phase out.
Any change to core functionality like window.postMessage() requires
extreme care, but the observed use of this overload is so low that the
risk of deprecating and actual removal seems acceptable. After
retirement, Safari will be the only browser supporting it.
Alternative implementation suggestion for web developers
Use window.postMessage(message, targetOrigin[, transferables])
Usage information from UseCounter
OWP launch tracking bug
Entry on the feature dashboard
Requesting approval to remove too?
Yes, M54 is the suggested milestone.