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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.lang.javascript
Subject: Re: How to manipulate integer that sometimes Nan and sometimes have a value?
Date: Tue, 29 Sep 2015 12:48:53 +0100
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jonas.thornvall@gmail.com writes:

> Den lördag 26 september 2015 kl. 21:51:43 UTC+2 skrev Ben Bacarisse:
<snip>
>> ...  An as yet
>> unassigned array position is undefined -- it won't have NaN as its
>> value.  However, isNaN (the global function by that name) converts it's
>> argument in such a way that undefined becomes NaN.
>> 
>>   $ nodejs
>>   > var a = [];
>>   undefined
>>   > a[1]
>>   undefined
>>   > a[1] === undefined
>>   true
>>   > isNaN(a[1])
>> 
>> This may be why you think you have NaN in the "extra" digit places.
>> 
>
> From what i understand an array, is a storage bin/stack of items. Now
> i have a stack of items that in most case do have an initiated element
> at index, but in some cases it is indeed empty.

Your terminology is wrong.  An array is not a stack and the metaphor of
describing as yet unused elements as empty is leading you astray.  They
are nether full nor empty -- an expression that accesses an unknown
property of an object has the value called undefined.  That's a value
like any other, and you can even assign it to an array element -- a[i]
may have been set to undefined.

> Since it is integer
> elements i do perform opeations upon performing carry operations, i
> think it is kind of weird that there is no good way to deal with this.

There is a way to deal with this.  You don't consider it a good way, but
there's nothing that can be done about that.

> This must be the most common problem programming statistics. I do not
> see why i should not be able to add to an undefined value, it is
> basicly like adding to zero. And since the type of the elements stored
> are integers, i just can't see the point i have to do a check
> everytime an assign a zero, it is ridiculous. A suggestion to fill the
> slot ahead with zeroes do not work either because then the array
> length will not report correct.

Not everyone has the same view of what is ridiculous.  I think what
ECMAScript does here is perfectly sensible.

> It is kind of strange that such operation report NaN back.

It's a reasonably choice for the language designers to have made.  You
might prefer to switch to Perl.  In Perl, undef() + 1 == 1 although it
is considered bad style to rely on that fact.

-- 
Ben.