=== again (sorry)

Allen Wirfs-Brock Allen.Wirfs-Brock at microsoft.com
Thu Nov 13 18:00:25 PST 2008


Now that this is pointed out the case that bothers me is code that looks something like this:

switch (num) {
        case NaN: alert("NaN");
        case +Infinity: case -Infinity: alert("Infinity");
        default: alert("a fine old number");
}

The intent of the code is obvious and yet the NaN case is obviously a bug.  However, I suspect that very view JavaScript programmer even among those who understand what a NaN is realize that.

I'd call this an attractive nuisance that should be fixed in the language specification, probably by changing switch to use Mark's SameValue test.

>-----Original Message-----
>From: es-discuss-bounces at mozilla.org [mailto:es-discuss-
>bounces at mozilla.org] On Behalf Of Igor Bukanov
>Sent: Thursday, November 13, 2008 9:18 AM
>To: Waldemar Horwat
>Cc: Mark S. Miller; es-discuss
>Subject: Re: === again (sorry)
>
>2008/11/11 Waldemar Horwat <waldemar at google.com>:
>> Mark S. Miller wrote:
>>>
>>> The indexOf and lastIndexOf methods are new in ES3.1, and are the
>only
>>> methods in the entire spec that depend on ===.
>>
>> Strictly speaking that's true, but only because the switch statement
>is not
>> a method.  switch statements depend on ===.
>
>There was a recently reported bug for SpiderMonkey where the
>implementation treated -0 as not equal to 0 for some optimized switch
>cases. Given that the bug was present in the code at least since 1998
>this gives indications that even for a switch a change to use
>Object.identical, not ===, could be compatible with the web.
>
>Regards, Igor
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