Yes, that is left unspecified in the spec:<p>* <a href="http:&#x2F;&#x2F;www.ecma-international.org&#x2F;ecma-262&#x2F;6.0&#x2F;#sec-allocatearraybuffer" rel="nofollow">http:&#x2F;&#x2F;www.ecma-international.org&#x2F;ecma-262&#x2F;6.0&#x2F;#sec-allocate...</a> (relevant: step 4, CreateByteDataBlock())