SharedArrayBuffer: cloning vs transferring?

Lars Hansen lhansen at
Wed Jan 25 14:03:18 UTC 2017

You're asking about how postMessage() handles a SharedArrayBuffer, since
the spec changed last summer from requiring the buffer to be in the
transfer list to forbidding it.  For the time being, Firefox allows the SAB
to be in the transfer list but prints a warning in the console; by and by
we will throw an error for that (and until then we'll fail any test cases
that test for an exception).  This is implemented in Firefox 51, if my
testing right now is correct.

Since no browser has officially shipped this functionality I think some
browser sniffing may be reasonable for early adopters who want to operate
in a multi-browser setting.  I would expect that when this functionality is
enabled by default in a browser the browser would adhere to the spec.


On Wed, Jan 25, 2017 at 10:49 AM, Axel Rauschmayer <rauschma at>

> AFAICT, all current implementations want you to transfer SABs. What’s the
> best way to prepare for the future? `try` transferring and clone in the
> `catch` clause?
> Thanks!
> Axel
> --
> Dr. Axel Rauschmayer
> [Sent from a mobile device, please forgive brevity and typos]
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