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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.lang.javascript
Subject: Re: sum array
Date: Sun, 12 Nov 2017 01:20:22 +0000
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Andrew Poulos <ap_prog@hotmail.com> writes:

> To sum the integer elements in an array I'm using
>
> var sum = arr.reduce(function(a, b) {
>   return a + b;
> });
>
> which is fine. When I pass it
>   var arr = [,0, 1, -1, 3,, null];
> I get the correct answer though I'm expecting it to error. Why doesn't
>   it throw an error or at least not the right answer?

First, reduce only considers the elements that are present in the array,
and second, null is converted to +0 before the addition (non-string operands
of + are converted to number using the the ToNumber abstract operation).

-- 
Ben.