Hi there,
Am 18.01.2009 um 18:45 schrieb Derrell Lipman:
> On Sun, Jan 18, 2009 at 11:55 AM, Mustafa Sak <m....@ims24-net.de>
> wrote:
>> Hi,
>>
>> it is possible, that IE puts automaticaly Elments in to a new Array
>> by default?
>>
>> i tried this
>>
>> var xx = new Array();
>> for (key in xx)
>> {
>> this.debug(key);
>> }
>>
>> In Firefox, i have no keys, like expected
>>
>> but at IE 6 i have this output:
>>
>> every
>> some
>> map
>> filter
>> forEach
>> lastIndexOf
>> indexOf
>>
>> Could this happen? Is there a work arround?
>
> qooxdoo adds these functions to the Array prototype to provide a
> consistent interface between browsers. Although it seems to work to
> iterate an Array use for/in, it's not technically legal.
Sorry, I disagree. It's perfectly legal to iterate over an array with
for ... in. In fact, it can be very useful to do so if you're working
with sparse arrays (where only a few indices are ever assigned a
value). Please keep in mind that there's not a lot that separates a
JavaScript Array instance from any arbitrary object (which is always
an associative array in JavaScript):
1.) Arrays have additional methods (like push()).
2.) For all _numeric_ keys that are used, the length property is set
to the value of the key + 1, provided the previous length value was
lower.
Consider the following example, which only works correctly in a non-
qooxdoo environment:
var x = new Array();
x[0] = 42;
for (var key in x) {
alert(typeof(key)); // result: string
}
x[2] = 43;
alert(x.length); // result: 3
The results make it pretty clear that arrays in JavaScript are not
that special (unlike in other programming languages). They're
basically associative arrays - and every key is automatically
converted to a string! -, and the length property is pretty "dumb".
This behaviour is also described in the ECMA spec, so it's not just a
random decision made by the browser developers. Yes, it can be
confusing, especially for JavaScript newcomers, but that's the way
this part of the language works.
> That paradigm is for objects, not arrays. Instead you should use
> indexes:
>
> for (var i = 0; i < xx.length; i++)
> {
> this.debug(i + ": " + xx[i]);
> }
As mentioned above, it can also be useful to iterate over an array
using for ... in. I think adding convenience methods to arrays is a
big mistake, even if they're present in other browsers. It can totally
screw array handling in some cases, and the benefits compared to
global functions or static methods are minimal (e.g. you could also
use indexOf(arrayInstance, obj) instead of arrayInstance.indexOf(obj)).
IMHO, the additional convenience you get by adding these methods to
the Array prototype are just not worth screwing with a core language
element (even if other browsers offer them natively, which means they
don't appear in for ... in iterations there).
Just my 2 cents,
Andreas J.
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