Are function arguments with the value `undefined` "present"?

Till Schneidereit tschneidereit at gmail.com
Fri May 31 07:50:59 PDT 2013


Hi David,

ah, thanks. That is indeed what I was looking for. Sadly, it isn't entirely
clear to me that any sort of real conclusion has been reached.


thanks,
till


On Fri, May 31, 2013 at 4:23 PM, David Bruant <bruant.d at gmail.com> wrote:

>  Hi Till,
>
> I believe Boris Zbarski touched on this recently at
> http://lists.w3.org/Archives/Public/public-script-coord/2013AprJun/0428.html(I haven't read the full thread, so can't tell what the conclusion were,
> but it's probably worth checking out)
>
> David
>
> Le 31/05/2013 04:33, Till Schneidereit a écrit :
>
>   I couldn't find any precise definition for the spec term "present", so
> this is not entirely clear to me.
>
>  Example:
> In step 7 of 15.4.3.21 Array.prototype.reduce, a TypeError must be thrown
> if the optional argument `initialValue` isn't present. If a value of
> `undefined` does *not* cause the argument to be present, that function can
> be implemented with the following signature:
>
> `function ArrayReduce(callbackfn, initialValue = undefined)`
>
>  If, however, the value `undefined` means that the argument is present,
> the signature should probably be:
>
> `function ArrayReduce(callbackfn, ...rest)`
>
>
>  The question isn't entirely academic, as I'm trying to get the
> self-hosted implementations of builtins in SpiderMonkey to be as close to
> the spec as possible.
>
>
> thanks,
> till
>
>
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>
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