Detached TypedArray access semantics

Allen Wirfs-Brock allen at
Wed May 6 15:59:23 UTC 2015

On May 6, 2015, at 7:36 AM, Daniel Ehrenberg wrote:

> In the draft ES6 spec, getting or setting array indices on detached TypedArrays raises a TypeError. However, both V8 and SpiderMonkey seem to return undefined from reads and silently succeed on writes. These semantics have probably been shipping for some time.
> As an implementer, I'm not sure what to do. Does anyone have any information on whether it'd break the web to throw an error in this case? What went into the decision to make these accesses throw an error in the spec rather than the Chromium/Mozilla semantics? If it would break the web, then should the spec be changed to match reality?

These issues were discussed at the June 2014 TC39 meeting, see 

"TC39 recognizes that the above are breaking changes relative to the Khronos spec. but we believe that the behavior of silently treating neutered buffers as 0-length buffers is seriously flawed and would set a terrible precedent for any future "transferable" data types."

As an implementor you should implement this change and expose it via your pre-production release channels.  Identify and analyze any breakage that is reported.  If there is limited breakage use evangelism to try to get web developers to change their dependency upon that behavior.  Report back to TC39 if you discover that breakage is wide-spread and cannot  be remediated. 


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