[NaN].indexOf(NaN) === -1 VS Object.is(NaN, NaN)

[Herby Vojčík]

Andrea Giammarchi wrote:
> just in case ... this is my internal function
>
>    // var is = Object.is || properShim
>    // var indexOf = [].indexOf || shortShim
>    // var i;
>    function betterIndexOf(value) {
>      if (value != value || value === 0) {
>        for (i = this.length; i-- && !is(this[i], value););

I always has the impression that indexOf is firstIndexOf not 
lastIndexOf... sometimes it matters.

Herby

>      } else {
>        i = indexOf.call(this, value);
>      }
>      return i;
>    }
>
> maybe somebody else should implement something similar to avoid N
> Object.is(a, b) checks within the loop ...
>
> cheers
>
> On Thu, Jun 14, 2012 at 1:59 PM, Andrea Giammarchi
> <andrea.giammarchi at gmail.com <mailto:andrea.giammarchi at gmail.com>> wrote:
>
>     This is basically what I am doing except I find Array#indexOf as it
>     is pointless ... or better, something that should be fixed in the
>     next version of ECMAScript.
>
>     Right now I am feature detecting the inconsistent behavior ... but a
>     feature detection that will never possibly return true is also
>     pointless ... thanks in any case :-)
>
>     br
>
>
>     On Thu, Jun 14, 2012 at 12:41 PM, Mark S. Miller <erights at google.com
>     <mailto:erights at google.com>> wrote:
>
>         Please replace your use of indexOf in your collection
>         implementations
>         instead. If indexOf is more efficient than one written in JS using
>         Object.is, then use the fast one when the argument is anything other
>         than NaN, 0, and -0.
>
>         On Thu, Jun 14, 2012 at 3:24 PM, Andrea Giammarchi
>         <andrea.giammarchi at gmail.com
>         <mailto:andrea.giammarchi at gmail.com>> wrote:
>          > Hello everybody,
>          >     I am not sure about the status of this subject but I find
>         quite
>          > inconsistent the fact we cannot trust Array#indexOf when it
>         comes to NaN ...
>          > I am updating my es6-collections shim accordingly with what
>         Paul Millr said:
>          > my shim does not consider NaN as a valid key, being unable to
>         find a match
>          > through indexOf, so each NaN key will result into a new one
>         for both Map and
>          > Set ( broken WeakMap too )
>          >
>          > I wonder if in the next future Array#indexOf will use
>         internally Object.is
>          > to compare values or if I have to use my own function to loop
>         over all
>          > values and do this kind of comparison.
>          >
>          > Any thought on this will be appreciated and apologies if this
>         has been
>          > discussed already ( so a quick answer on "how it's going to
>         be" would be
>          > more than enough )
>          >
>          > Best Regards,
>          >     Andrea Giammarchi
>          >
>          > _______________________________________________
>          > es-discuss mailing list
>          > es-discuss at mozilla.org <mailto:es-discuss at mozilla.org>
>          > https://mail.mozilla.org/listinfo/es-discuss
>          >
>
>
>
>         --
>              Cheers,
>              --MarkM
>
>
>
>
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