312759 - Javascript error. For in array bug, returning 'indexOf' as last element of array, even when array is empty

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[Alex]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050922 Firefox/1.0.7 (Debian package 1.0.7-1)
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050922 Firefox/1.0.7 (Debian package 1.0.7-1)

When i am using the 'for (item in array)' even when the array is empty, firefox
returns a elment called 'indexOf' as last item of that array.

Reproducible: Always

Steps to Reproduce:
1. Write a javascript code to create an empty array 
2. Use the code "for (item in array)" to navigate in the array.
3. User "alert(item)" in every loop to see the non-existent element "indexOf"

Actual Results:  
Firefox return one more item that does not exists

Expected Results:  
No "indexOf" item on the array

Comment 1

[Josh Birnbaum]

->js engine

Comment 2

[Brendan Eich [:brendan]]

Linux_All_DBG.OBJ/js
js> a = []

js> for (i in a)print(i)
js>

Worksforme.  Please give a complete testcase.

/be

Comment 3

[Blake Kaplan (:mrbkap) (inactive)]

Brendan, this is reported against the 1.7 branch (does that make it FIXED?
INVALID? WONTFIX (not a security bug)?).

Comment 4

[Blake Kaplan (:mrbkap) (inactive)]

Actually, I can't even reproduce this in a 1.7 build. I guess a full testcase is
needed.

Comment 5

[Brendan Eich [:brendan]]

Right, I tried my SpiderMonkey build from AVIARY_1_0_1_20050124_BRANCH and it
works as expected.  We need a testcase file attached to this bug.

/be

Comment 6

[Alex]

What happends is that when I add a new function to an array prototype, doing that: 

 Array.prototype.getLast = function() {
        return this[this.length-1];
    }

and do the "for (item in array)" on an array, that function are returned as an
array element. Is that right? Is that the way mozilla should respond???

Comment 7

[Brendan Eich [:brendan]]

This bug is confusingly summarized and reported.  The problem is not the
built-in indexOf method being enumerable by for-in loops over arrays.  The
reported problem is that a user-defined property is enumerable.  That's how JS
works, however, so INVALID.  If you want to enumerate only the elements (indexed
properties), use a for (i = 0; i < a.length; i++) loop.

/be