Classes

[unwantedspam]

I am getting an "Object Expected" error on line 0. Do you see anything
wrong with the following code:

var iTest = 60

function test(msg)
{
var NewMessage = msg;
StartIt(NewMess age);
function DisplayMessage( theMessage)
{
alert(iTest + theMessage);
}

function StartIt(theMess age)
{
var timer;
timer = setInterval("Di splayMessage('" + theMessage + "')",2000);
}

}
Thank you in advance

The email address is valid.

[RobG]

un**********@mc hsi.com wrote:

I am getting an "Object Expected" error on line 0. Do you see anything
wrong with the following code:
Because DisplayMessage( ) is defined as a local variable of test().
setInterval() attempts to run it from a global context so it can't find it.

var iTest = 60

function test(msg)
{
var NewMessage = msg;
Varialbes starting with a capital letter usually signifies that they
will be used as a constructor - just a convention.

StartIt(NewMess age);
function DisplayMessage( theMessage)
{
alert(iTest + theMessage);
}

function StartIt(theMess age)
{
var timer;
timer = setInterval("Di splayMessage('" + theMessage + "')",2000);
var timer = setInterval(fun ction(){
DisplayMessage( theMessage);
},2000);
However that creates a closure and may cause memory leak problems in
some (buggy) browsers.

}

}

--
Rob

[Thomas 'PointedEars' Lahn]

un**********@mc hsi.com wrote:

I am getting an "Object Expected" error on line 0. Do you see anything
wrong with the following code:
Plenty. However, let us begin with the fact that there are no classes in
the language version you use.
var iTest = 60
Avoid global variables.
function test(msg)
{
var NewMessage = msg;
This variable declaration is redundant, `msg' is already a local variable.
StartIt(NewMess age);
function DisplayMessage( theMessage)
{
alert(iTest + theMessage);
}

function StartIt(theMess age)
{
var timer;
timer = setInterval("Di splayMessage('" + theMessage + "')",2000);
}

}
DisplayMessage( ) and StartIt() are inner functions of test(). They are
not a method of `test' objects, nor is there a `test' class (see above).
setInterval() is in fact the same method as window.setInter val() which
evaluates its argument in global context always. However, because
DisplayMessage( ) is not defined in global context, only in the local
one if test(), you get the useless error message from Internet Explorer.
(Try the JavaScript/Error Console a Gecko-based or Opera-based browser
instead. See also <URL:http://jibbering.com/faq/#FAQ4_43>.)

A reasonable solution would include proper application of prototype-based
inheritance, something like

function Test(msg)
{
this.test = 60;
this.startIt(ms g);
}

Test.prototype = {
displayMessage: function test_displayMes sage(theMessage )
{
alert(this.test + theMessage);
},

startIt: function test_startIt(th eMessage)
{
this.timer = window.setInter val(
function()
{
this.displayMes sage(theMessage );
},
2000);
}
};
Test.prototype. constructor = Test;

var t = new Test("foo");

Caveat: This will not work in IE before version 5.0, and NN before
version 1.3. <URL:http://pointedears.de/scripts/js-version-info>

You will find that yours is quite a FAQ here. Please do research
before you post.
The email address is valid.

True, however a name would be nice. I, for one, do not like talking
to e-mail addresses (or companies); I like talking to people :)
PointedEars

[unwantedspam]

Thomas 'PointedEars' Lahn wrote:

un**********@mc hsi.com wrote:

I am getting an "Object Expected" error on line 0. Do you see anything
wrong with the following code:

Plenty. However, let us begin with the fact that there are no classes in
the language version you use.

var iTest = 60

Avoid global variables.

function test(msg)
{
var NewMessage = msg;

This variable declaration is redundant, `msg' is already a local variable.

StartIt(NewMess age);
function DisplayMessage( theMessage)
{
alert(iTest + theMessage);
}

function StartIt(theMess age)
{
var timer;
timer = setInterval("Di splayMessage('" + theMessage + "')",2000);
}

}

DisplayMessage( ) and StartIt() are inner functions of test(). They are
not a method of `test' objects, nor is there a `test' class (see above).
setInterval() is in fact the same method as window.setInter val() which
evaluates its argument in global context always. However, because
DisplayMessage( ) is not defined in global context, only in the local
one if test(), you get the useless error message from Internet Explorer.
(Try the JavaScript/Error Console a Gecko-based or Opera-based browser
instead. See also <URL:http://jibbering.com/faq/#FAQ4_43>.)

A reasonable solution would include proper application of prototype-based
inheritance, something like

function Test(msg)
{
this.test = 60;
this.startIt(ms g);
}

Test.prototype = {
displayMessage: function test_displayMes sage(theMessage )
{
alert(this.test + theMessage);
},

startIt: function test_startIt(th eMessage)
{
this.timer = window.setInter val(
function()
{
this.displayMes sage(theMessage );
},
2000);
}
};
Test.prototype. constructor = Test;

var t = new Test("foo");

Caveat: This will not work in IE before version 5.0, and NN before
version 1.3. <URL:http://pointedears.de/scripts/js-version-info>

You will find that yours is quite a FAQ here. Please do research
before you post.

The email address is valid.

True, however a name would be nice. I, for one, do not like talking
to e-mail addresses (or companies); I like talking to people :)
PointedEars

Thank you both for your replies. I have learned a lot. I greatly
appreciate it.

Thanks again,
Kent

[unwantedspam]

After implementing the code you provided I got the following error:
Line 19 Object doesn't support this property or method.
Line 19 is:
this.displayMes sage(theMessage );
If I change this to:
test_displayMes sage(theMessage );
it almost works. The error goes away but I get undefinedfoo. I would
assume this means the code doesn't "see" test = 60. Why would this be?
Also, is the change I made, the correct change to the code?

Thanks again for you help,
Kent

[Lasse Reichstein Nielsen]

Thomas 'PointedEars' Lahn <Po*********@we b.de> writes:

A reasonable solution would include proper application of prototype-based
inheritance, something like

function Test(msg)
{
this.test = 60;
this.startIt(ms g);
}

Test.prototype = {
displayMessage: function test_displayMes sage(theMessage )
{
alert(this.test + theMessage);
},

startIt: function test_startIt(th eMessage)
{
this.timer = window.setInter val(
function()
{
this.displayMes sage(theMessage );
The "this" operator in this context will refer to the global object as
well, when the function is called by the setInterval timer.

A way to capture the correct value in the closure would be:
...
var self = this;
this.timer = window.setInter val(
function() {
self.displayMes sage(theMessage );
...

},
2000);
}
};
Test.prototype. constructor = Test;

This could be moved into the object literal too, or instead of
assigning to the prototype property, one could assing properties to
the existing prototype object, which already has this value.

/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

[VK]

Lasse Reichstein Nielsen wrote:

A way to capture the correct value in the closure would be: ...
var self = this;

"self" is a property of window object (self-reference to the current
window):
self.alert('OK' ); // equals window.alert('O K') in the global scope

Usually it is not recommended to override host object properies unless
required by the augmentation logic.

To fix the "incontinen ce of this" issue I would suggest to use some
unifirmed identifier instead - like $ (just a suggestion).

[Michael Winter]

On 01/03/2006 07:45, VK wrote:

Lasse Reichstein Nielsen wrote:

A way to capture the correct value in the closure would be:
...
var self = this;
"self" is a property of window object (self-reference to the current
window):

What exactly does that have to do with anything? The variable defined
above will be a local variable; a property of the Variable object for
the test_startIt function. Resolution of this identifier through the
scope chain will find it in that location before the global object is
reached and searched.
self.alert('OK' ); // equals window.alert('O K') in the global scope
No-one denies that in most object models, both the self and window
global variables refer to the global object. It's just that most will
realise that it's irrelevant in this scenario.
Usually it is not recommended to override host object properies
unless required by the augmentation logic.
The global variable will not be overwritten.
To fix the "incontinen ce of this" issue I would suggest [...]

I would suggest that you learn to understand how ECMAScript-based
languages work before trying to correct others.

Mike

--
Michael Winter
Prefix subject with [News] before replying by e-mail.

[VK]

Michael Winter wrote:

I would suggest that you learn to understand how ECMAScript-based
languages work before trying to correct others.

I'm sorry, but you may drop this paternizing tone with me. Richard
alone is more then enough - "the horse cannot hold both" :-)

Please: I did *not* say that the posted code will not work - it will. I
just questionned the real need to shadow the global "self" reference in
the function.

[Michael Winter]

On 01/03/2006 12:40, VK wrote:

[snip]

Please: I did *not* say that the posted code will not work - it will.
But you did imply that it will "override host object properies [sic]",
when such a statement is quite simply false.
I just questionned the real need to shadow the global "self"
reference in the function.

You haven't made a case for why it should be avoided. There is no direct
reference to the global object at all, let alone through a global
'self'. The word 'self' as an identifier is quite appropriate in this
case, and it isn't so frequently used nor important enough that its
redefinition would be confusing (as might be the case with 'document' or
'window', for example).

Mike

--
Michael Winter
Prefix subject with [News] before replying by e-mail.