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From: Thomas 'PointedEars' Lahn on 6 May 2008 18:26
Tom Cole wrote:
> Javascript arrays are a little tricky in this regards. Yes you can
> "name" and Array entry, or more accurately assign a "name" as the key.
> The problem is, in my experience, that when store array elements in
> this manner, the length of the array is not adjusted.

Because you are not storing array elements then, but augment the Array object.

> For example this is totally legit:
>
> var images = new Array();
> images['Massey 2007'] = "ecwp://" + document.location.host + "/massey/
> images/massey/massey_07_fullres.ecw";
> images['Massey 2006'] = "ecwp://" + document.location.host + "/massey/
> images/massey/massey_06_fullres.ecw";

And why not? Array objects are native objects and, some properties with the
ReadOnly attribute aside, native objects can be augmented with any number of
properties.

> However if you call alert(images.length) you will get 0.

It helps to use a collection implementation instead.

> Of course even if it didn't, this wouldn't help, because you need the key (or
> "name") not just the value. And there is no method that I have found
> to retrieve the list of keys an array is using.

var a = ["x", 42];
a["foo"] = "bar";

var out = [];

for (var key in a)
{
var p = a[key];
var t = typeof p;
if (t == "string")
{
p = '"' + p.replace(/"/g, "\\$&") + '"';
}

out.push(key + ": " + t + " = " + p);
}

// displays the enumerable properties of `a'
// and the objects in its prototype chain
window.alert(out.join("\n"));

Note that this can be useful with a collection implementation; if a
collection is not required, then one should use an Object object
instead of an Array object.

> So...the problem isn't "naming" your array elements, but how do you
> remember that list of names so you can later retrieve the values.

Provided one does not augment Object.prototype or Array.prototype, it is not
as hard to implement as you think.

> You will probably need two arrays, one to store the "names" and the
> other to store the "values".

No, this is not necessary. You can create user-defined objects that are
elements of the array instead.


PointedEars
--
realism: HTML 4.01 Strict
evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann
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