Thanks for clearing it up, it makes more sense like this.
So this should be considered as a feature of JavaScript rather than a
Prototype bug.
I spent about half a day debugging a Class because of that
feature... ;-)
Regards,
Tobie
On 25 oct. 2006, at 03:14, Christophe Porteneuve wrote:
>
> Hey Tobie,
>
> Ah, I should have waited for breakfast caffeine to sink in before
> answering you, sorry :-)
>
> Prototype-defined fields are *not* static fields /per se/. You would
> have to work on the constructor function's prototype to obtain
> something
> along those lines.
>
> The issue you run into here is due to how prototypes are used by
> the new
> operator. Basically, every instance refers, by default, to the
> properties defined in the prototype, dynamically. It's like they
> automatically proxy-delegate to the prototype, with the "this" binding
> going on for methods.
>
> Don't forget that object variables are just references. If you do
> this
> in JavaScript:
>
> var a = [1, 2, 3];
> var b = a;
> a[1] = 'X';
>
> Then b will become [1, 'X', 3]. The "b = a" expression just copies a
> pointer, so to speak. Both variables reference the same object.
>
> It's fortunate that prototypes work this way, otherwise each instance
> would hold, for instance, a distinct copy of all methods and fields
> defined in the prototype. Which would be a pretty bad way to go about
> defining methods.
>
> When you want per-instance fields that are still object references,
> you
> need to assign them to "this."-prefixed properties in the initialize
> function (called at construction time, see Class.create). This way,
> each "new", calling initialize, will use a fresh value (i.e. a fresh
> object) for its field, therefore a unique reference.
>
> Look into Prototype and script.aculo.us code: you'll see that all
> prototype-defined fields are basically used as constants (e.g. the
> NODEMAP and ATTR_MAP fields in Builder). All per-instance fields are
> assigned, directly or indirectly, from the initialize functions.
>
> As for this code:
>
> Tobie Langel a écrit :
>>>> var Tester = Class.create();
>>>> Tester.prototype = {
>>>> initialize: function(str) {
>>>> this.string = str;
>>>> },
>>>> string: ''
>>>> }
>
> The last string definition is useless: it's going to be overridden
> locally by every instance, because of the initialize function, that
> guarantees each instance has its own reference.
>
> I hope this makes it a bit clearer.
>
> --
> Christophe Porteneuve aka TDD
> [EMAIL PROTECTED]
>
> >
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