Javascript confusion....

[George Ter-Saakov]

I am trying to get into depth of JavaScript a little more and find it a bit
confusing for person who is used to C#/C++ object oriented approach..

So I need some help in understanding how staff works... Given following
object definition

ZColor = function(num)
{
var a = num + 1;
this.b = num + 2;
this.show = function()
{
alert(a);
alert(this.b);
}
}



I have folowing code that runs when htm page is loaded.

var obj = new ZColor(6);
setInterval(obj .show, 1000);

So it produces 2 alerts. First is "7" and second is "undefined"
So basically show method has access to "a" variable and does not have access
to "b" variable...

I do understand why "alert(this .b)" does not work from timer function. Cause
timer has not idea that i want to run it under "obj" as "this" scope.

But what puzles me is why "alert(a)" works... .

Thanks
George.

[Anthony Jones]

Re: Javascript confusion....

"George Ter-Saakov" <gt-nsp@cardone.com wrote in message
news:eHxnqB8fIH A.4196@TK2MSFTN GP04.phx.gbl...

Thanks, I did not have exposure to any of those languages "ruby,

python,.."

So that thing is quite new for me.
>
The parallel you made between closure and delegates does help although it
seems to me the "closure" is much "bigger" in terms of functionality.
On the other hand I do not see much use of it (right now) except imitating
delegates :)
>

One use is to solve the 'this' problem you identified:-

ZColor = function(num)
{
var a = num + 1;
this.b = num + 2;
this.show = function()
{
alert(a);
alert(this.b);
}
}

function setInterval3(fn , period, target)
{
setInterval(fun ction() {fn.call(target )}, period)
}

var obj = new ZColor(6);
setInterval3(ob j.show, 1000, obj);

In this case the alert(this.b) will now work


--
Anthony Jones - MVP ASP/ASP.NET