Subj : Re: JSVAL_IS_NUMBER(NaN) == TRUE (!?)
To   : Justin Fletcher
From : Rob Swindell
Date : Mon Feb 21 2005 12:42 am

  Re: Re: JSVAL_IS_NUMBER(NaN) == TRUE (!?)
  By: Justin Fletcher to netscape.public.mozilla.jseng on Sun Feb 20 2005 04:08 pm

 > >  > > I found it odd that if jsval is NaN, a test of JSVAL_IS_NUMBER(jsval)
 > >  > > evaluate as TRUE.
 > >  >
 > >  >
 > >  > Sure, it's of "number" type (see also typeof(0/0)).
 > >
 > > It just seemed illogical (to me) that:
 > >
 > >         is (not a number) a number?
 > >
 > > would evaluate to a true statement.
 > 
 > As Brendan just said - that's not the question that you're asking with
 > that statement, though.
 > 
 > JSVAL_IS_NUMBER(jsval) asks :
 > 
 >    is the intrinsic type of (jsval) a numeric type ?
 > 
 > NaN is a numeric type value.
 > 
 > JSVAL_IS_* is used at the lowest level for determining the type of data
 > represented by a 'jsval'. It places no interpretation on the content of
 > the data, if it is of that type. That there is particular representation
 > within the type 'double' which indicates that the value is not a
 > valid number is irrelevant to it.
 > 
 > The documentation I have here (albeit a little dated) says this in a
 > slightly more succinct manner :
 > 
 > " Use JSVAL_IS_NUMBER to determine if a given JS value, v, is an integer
 >   or double value. If the type tag for v is JSVAL_INT or JSVAL_DOUBLE,
 >   JSVAL_IS_NUMBER evaluates to true. Otherwise, it evaluates to false. "

It doesn't mention NaN, but I get the concept. Thanks. :-)

                                                  digital man

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