Class Problem

[Jim Red]

Hello NG

I have a problem with classes in javascript. When I define my class and
make an instance more than one time, it does not contian their own
variables:

var Counter = (function() {
var counter = 0;

function Constructor() {
this.fncInit();
}

Constructor.prototype.fncInit = function() {
counter++;
alert(counter);
}
})();

var counter1 = new Counter();
var counter2 = new Counter();
var counter3 = new Counter();

The counter increases by one each time, but it should always be 1.

Thanks for any help.

Jim

[Michael Winter]

On 20/06/2005 15:19, Jim Red wrote:

I have a problem with classes in javascript.
You certainly do: there are no classes. ECMAScript works within a
prototype object model, not a class-based one.
When I define my class and make an instance more than one time, it does not contian their own
variables:

var Counter = (function() {
var counter = 0;

function Constructor() {
this.fncInit();
}
The counter variable here is effectively a private static member.
Instead, use:

function Counter() {
var counter = 0;

this.fncInit = function() {
++counter;
alert(counter);
};

this.fncInit();
}

[snip]
})();

You don't actually return the Constructor function in the posted code.
This would mean there is no function with which to apply the new
operator. Did that arise because you didn't type it into the post, or
did the return statement not appear in the original, either?

var MyObject = (function() {
/* Private static variables and methods here */

function constructor() {
/* Private instance variables and methods,
* and public 'priviledged' methods here.
*/
}
/* Public static (assigned directly to
* constructor) and prototyped variables and
* methods here
*/

return constructor;
})();

[snip]

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

[Jim Red]

Michael Winter wrote:

On 20/06/2005 15:19, Jim Red wrote:

I have a problem with classes in javascript.

You certainly do: there are no classes. ECMAScript works within a
prototype object model, not a class-based one.

When I define my class and make an instance more than one time, it
does not contian their own variables:

var Counter = (function() {
var counter = 0;

function Constructor() {
this.fncInit();
}

The counter variable here is effectively a private static member.
Instead, use:

function Counter() {
var counter = 0;

this.fncInit = function() {
++counter;
alert(counter);
};

this.fncInit();
}

[snip]

})();

You don't actually return the Constructor function in the posted code.
This would mean there is no function with which to apply the new
operator. Did that arise because you didn't type it into the post, or
did the return statement not appear in the original, either?

oops, sorry. I forgot about it.
//Jim

var MyObject = (function() {
/* Private static variables and methods here */

function constructor() {
/* Private instance variables and methods,
* and public 'priviledged' methods here.
*/
}
/* Public static (assigned directly to
* constructor) and prototyped variables and
* methods here
*/

return constructor;
})();

[snip]

Mike