Well, it depends upon implementations actually adhering to the typeof specification (which may take some time to come about). In ES5 IsCallable is a specification device that essentially means you really truly can call it (which is what it means to have a [[Call]] specification method).
Allen
>-----Original Message-----
>From: Mark S. Miller [mailto:
erights@...]
>Sent: Friday, June 05, 2009 2:19 PM
>To: Allen Wirfs-Brock
>Cc: Garrett Smith; es-discuss
>Subject: Re: Using IsCallable Operation?
>
>On Fri, Jun 5, 2009 at 1:39 PM, Allen Wirfs-Brock
><
Allen.Wirfs-Brock@...> wrote:
>> Not in ES5. Generally checking that typeof x === 'function' is a
>close approximation. ES5 (11.4.3) requires that both native (ie, pure
>actual ECMAScript objects) and host objects that implement [[Call]]
>produce "function" when typeof is applied to them. This is a change
>from ES3 that did not impose this requirement upon host object objects.
>
>Why is this an approximation? In ES5, how can
> typeof x === 'function'
>differ from testing whether something is callable?
>
>--
> Cheers,
> --MarkM
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