Is this a bug? Nonmatching capturing parens in regexp in replace with function are not undefined in Firefox
 

In this code:

function see(wot) {
var a = "0: " + arguments[0];
for (var i = 1; i < arguments.length; i++)
a += "\n" + i + ": " + arguments[i];
alert(a);
return wot;
}

"There is food at the bar".replace(/(foo)|(bar)/g, see)

In Firefox 2, you see 2 alert boxes with respective contents:

0: foo
1: foo
2:
3: 9
4: There is food at the bar

0: bar
1:
2: bar
3: 21
4: There is food at the bar

The non-matching capture (arguments[2] in the first case, arguments[1]
in the second) is the empty string, but defined. That makes it very hard
to see if a capture did match the empty string, as opposed to *not*
matching.

In MSIE6 and Opera9 I see almost the same, but with an essenstial
difference:

0: foo
1: foo
2: undefined
3: 9
4: There is food at the bar

0: bar
1: undefined
2: bar
3: 21
4: There is food at the bar

If you turn it inside out, with

/(foo)|(bar)/.exec("There is food at the bar")

Then, in Firebug, you see:

["foo", "foo", undefined]

which is the proper result.

Safari 3 beta appears to show the same results as Firefox.

What do you think... bug? I think it is... Where to report it?

--
Bart.

Re: Is this a bug? Nonmatching capturing parens in regexp in replace with function are not undefined in Firefox
 

On Sep 2, 4:04 pm, Bart Lateur <bart.lat...@pandora.be> wrote:
> What do you think... bug? I think it is... Where to report it?
>
> --
> Bart.

I think that's been reported:

https://bugzilla.mozilla.org/show_bug.cgi?id=389717

Re: Is this a bug? Nonmatching capturing parens in regexp in replace with function are not undefined in Firefox
 

Ed wrote:

>I think that's been reported:

Thanks. It looks like it is indeed the exact same problem.

--
Bart.