super.prop assignment can silently overwrite non-writable properties

Kevin Smith zenparsing at
Tue Apr 21 03:25:39 UTC 2015

> 5.e If *existingDescriptor* is not *undefined*, then
>        i.   If IsAccessorDescriptor(*existingDescriptor*), return *false*.
>        ii.  If *existingDescriptor*.[[Writable]] is *false*, return
> *false*.
>        iii.  Let *valueDesc* be the PropertyDescriptor{[[Value]]: *V*}.
>        iv.  Return *Receiver*.[[DefineOwnProperty]](*P*, *valueDesc*).
> Lines 5.e.i and 5.e.ii are new additions.

Looks good to me.

Thanks, Jason, for bringing this up!
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