Rob, that's a great explanation, thanks. You're right, I see now how
using the prototype keyword makes it clearer what is part of the
class, and what is part of the instance.
In the below example, I have to put the instruction to create the
behaviours of the Man and Woman in each of their constructors.
However, Man and Woman are both subclasses of the Person class - how
can I get this instruction into the Person class?
Cheers again!
----------------------------------------------------------------------------
var Behaviours = Class.create({
initialize: function() {
this.array=[];
},
push: function(behaviour) {
this.array.push(behaviour);
},
list: function() {
$A(this.array).each(function(behaviour) {
alert(behaviour);
});
}
});
var Person = Class.create({});
var Man = Class.create(Person, {
initialize: function () {
this.name = 'Iain';
this.behaviours = new Behaviours();
this.behaviours.push('eat');
}
});
var Woman = Class.create(Person, {
initialize: function () {
this.name = 'Ailsa';
this.behaviours = new Behaviours();
this.behaviours.push('talk');
}
});
On Jan 18, 7:13 am, RobG <[EMAIL PROTECTED]> wrote:
> On Jan 18, 2:30 am, iporter <[EMAIL PROTECTED]> wrote:
>
>
>
> > In the below code, I expect two alerts '1 : 1' and then '1 : 1', but
> > in reality I get '1 : 1' and '2 : 1'. For some reason, the
> > declaration of the second object of class myClass alters the first
> > object of the same class. However, it only alters
> > 'this.options.value', and not 'this.value'. Can you tell me why this
> > behaviour occurs, and how to resolve it?
>
> > Cheers
>
> > ---------------------------------------------------------------------------
> > var myClass = Class.create({
> > options:{},
> > value: false,
> > initialize: function(options) {
> > this.options.value = options.value;
> > this.value = options.value;
> > },
> > myAlert:function() {
> > alert(this.options.value + ' : ' + this.value);
> > }
>
> > });
>
> > var classObj1 = new myClass({value:1});
> > classObj1.myAlert();
> > var classObj2 = new myClass({value:2});
> > classObj1.myAlert();
>
> I think you are better off to understand what is actually happening.
> Javascript does not have classes - it isn't an object oriented
> language, it's object based. It uses prototypes for inheritance, not
> classic OO inheritance.
>
> While you can paper over the differences, they are still there. Two
> features that often cause issues are the this keyword and closures,
> which have combined here to cause an unexpected result.
>
> To write your "class" (it's actually a javascript constructor, but
> whatever) using plain javascript, you would write something like:
>
> function MyClass(obj) {
> this.value = obj.value;}
>
> MyClass.prototype.options = {};
> MyClass.prototype.showValue = function(){
> alert(this.options.value + ':' + this.value);
>
> }
>
> That's it. Note that this takes less code than using Class.create().
> Now if you test this:
>
> var x = new MyClass({value:1});
> x.showValue(); // --> 1:1
>
> var y = new MyClass({value:2});
> x.showValue(); // --> 2:1
>
> You get the result you didn't want - the options object is shared by
> all instances of MyClass because it is a property of the constructor's
> prototype. If you want each instance of MyClass to have its own
> options object, you add it in the constructor:
>
> function MyClass(obj) {
> this.value = obj.value;
> this.options = {};
> this.options.value = this.value; // or obj.value;}
>
> MyClass.prototype.showValue = function(){
> alert(this.options.value + ':' + this.value);
>
> }
>
> Now when you create some instances:
>
> var x = new MyClass({value:1});
> x.showValue(); // --> 1:1
>
> var y = new MyClass({value:2});
> x.showValue(); // --> 1:1
> y.showValue(); // --> 2:2
>
> Is that what you wanted? To me, the above is much simpler and clearer
> than using Class.create, and is less code.
>
> --
> Rob
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