Array Generics and null

Mike Shaver mike.shaver at
Mon Mar 24 05:36:29 PDT 2008

On Sun, Mar 23, 2008 at 2:44 AM, Dean Edwards <dean at> wrote:
>  I'd prefer Array.forEach(null) to do nothing, just like for (var i in
>  null) does nothing. I'm prepared to be convinced otherwise. :-)

forEach isn't like enumeration, though, it's like the more common
Array pattern of

for (var i = 0; i < a.length; i++) {

And if a is |window|, you get exactly the same effects, no?  If a is
null, you get an exception, which I think is probably not what we
want.  FWIW, ES3 specifies that |for (var i in null)| throw a
TypeError (see 12.6.4 step 3, and 9.9), but we and AFAIK all other
browsers intentionally diverge; we made that change relatively
recently, I think in FF2's timeframe.  I expect that ES4 will specify
the non-throwing behaviour, because an exception is just too harsh a
punishment for trying to iterate over null or undefined.


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