ged wrote:
> i am a oo (c#) programmer,
Your shift key seems to be intermittent. If you are going to attempt to
engage in written communication (or computer programming for that
matter) it may prove advantageous to have your keyboard serviced or
replaced.
> and have not used javascript for a while and i cant work
> out how javascript manages its references.
Javascript leaves the mechanism of references to objects up to the
implementers. The only important detail is that when an object property
is assigned the value 'of an object' the resulting value refers to that
object, and when a value that is 'of an object' is passed as an argument
to a function call it is the value that refers to the object that is
passed (the functions formal parameter will refer to the same object
instance).
> Object References work for simple stuff, but once i have an
> object collection and stanrd using it it starts to fall apart.
Implementations are consistent in the way that they handle object
references (that is, the resulting behaviour is consistent) so that is
likely to follow from some misconception.
> Clearly there is something about javascript's usage of
> passing "By ref" that i am not getting.
And an explanation if what it is that you are expecting is probably the
best way of getting an explanation of where your expectations do not
corresponds with reality.
> i have had a look on the web and found some examples, but
> i cant see why my code does not work.
But your code does work, in the sense that it does exactly what you have
programmed it to do. So the question becomes; what is it that you want
it to do? or; what would qualify as working?
> Grrrrh. I really need to know why because i am writng a large
> app in javascript and Ajax.
AJAX implies javascript.
> I program in c# mainly and i am applying soem OO principles
> to my javascript but i am goign nust with how its works
> sometimes.
>
> Also on a side not i dont get why i code javaScript this way
> to make it work?
>
> var personEntity = new PersonEntity("ged", 35);
> document.write(personEntity.Name;
>
> function PersonEntity(name, age)
> {
> var Name = name;
> var Age - age;
> }
Assuming that the subtraction operation is a typo (or another symptom of
your defective keyboard), this is a futile function as a function's
formal parameters, local variables and inner function declarations
result in the creation of named properties of the 'Activation/Variable'
object that sites at the top of the scope chain form the execution of
the function body. The Activation/Variable object is only accessible
through the scope chain. (See ECMA 262, 3rd edition; Sections 10.1.4 and
10.2)
Any object created with this constructor4 will not have a public 'Name'
property, so the document.write above would output 'undefined'.
> it has to be instead:
> function PersonEntity(name, age)
> {
> this.Name = name;
> this.Age = age;
> }
The - this - keyword refers to the object being constructed when this
function is used as a constructor. You create a 'Name' property of that
object and assign a value to it, so the document.write will wrote out
the value of that property.
> i have a sneaking suspicion that the above example also has
> something to do with my misunderstanding of the javascript
> reference pointers work.
Looks like you need to understand javascript's scopeing, identifier
resolution and the looking up/creation of properties on objects. Try:-
<URL:
http://www.jibbering.com/faq/faq_notes/closures.html >
> Code is below as a complete test. You just have to save it
> and load into your browser and it will run telling you where
> it errored. I really want an answer on this and am trying to
> make it easy for someone to tell me why is DOES NOT WOKR .
Would it have been so much effort to actually write down what the error
was and indicate which line produced it. The error reported by IE is
"'appItem' is undefined" (line 96, char 9). That line is inside of the -
SetCurrentItem - method of the - AppModel - object. And it happens
because there is no object on the scope chain of that method with a
property named 'appItem'.
> thansk in advance
>
> Ged
>
>
> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
> "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
> <html xmlns="http://www.w3.org/1999/xhtml">
Yikes, an XHTML doctype. You don't want to be scripting XHTML in a
commercial context as the additional effort required to accommodate IE's
lack of support for XHTML considerably exceeds the negligible returns in
using that type of mark-up.
> <head>
> <title>Reference Test</title>
>
>
> <script language="JavaScript">
In valid (x)HTML the LANGUAGE attribute of SCRIPT elements is deprecated
and the TYPE attribute is required.
<script type="text/javascript">
<snip>
> function AppController()
> {
> // App Icon clicked
> this.AppItemLoadCommand = function(id)
> {
>
> // resolve item clicked
> var appItem = g_appModel.GetAppItemByIconElementId(id);
>
> document.write("appItem.appIconElementId : " +
This is a significant problem is you int4end attempting to use XHTML as
no current XHTML DOM implementation supports the document.write method.
That is, if there is any chance of this document ever being interpreted
as anything other than error-filled HTML the code will instantly break
as the document.write calls will fail.
> appItem.appIconElementId + "<BR />");
And if this document is intended to be served as 'text/html' and so
interpreted as error-filled HTML, error corrected back to tag-soup HTML,
and an HTML DOM created from the result (so that the document.write
method will work at all) there is little point in document.writie-ing
XHTML style mark-up. Doing so is just irrational.
> // Set Model
> g_appModel.SetCurrentItem(appItem);
>
> // Set View
> var appView = AppView();
> appView.SetFocus(g_appModel.appList, appItem);
> }
> }// JScript File
It is a universally good idea to indent source code (and do so
appropriately when posting code to newsgroups, i.e. with spaces instead
of tabs). Here you have the call to the SetCurrentItem - method that
results in the error. The local variable 'appItem' has its value passed
as the argument to the method call.
> function AppModel()
> {
> this.currentItem = null;
> this.appList = new Array();
>
> this.Add = function(appItem)
> {
> this.appList[this.appList.length] = appItem;
> };
This inner function expression will result in the creation of a new
function object and the assignment of a reference to that new function
object to th4e 'Add' property of this object instance. The same process
is repeated for each instantiation of an instance of 'AppModel'. The
function created is not exploiting its status as an inner function and
so there is no need for each instance of 'AppModel' to have a distinct
function object instance as its 'Add' method.
> this.GetAppItemByIconElementId = function(id)
> {
> for(var x=0; x < this.appList.length; x++)
> {
> if(this.appList[x].appIconElementId == id)
> {
> return this.appList[x];
> }
> return null;
> }
> }
The same as above applies to this 'GetAppItemByIconElementId' method.
> this.GetAppItemByPanelElementId = function(id)
> {
> for(var x=0; x < this.appList.length; x++)
> {
> if(this.appList[x].appPanelElementId == id)
> {
> return this.appList[x];
> }
> return null;
> }
> }
The same as above applies to this 'GetAppItemByPanelElementId' method.
> this.SetCurrentItem = function(appitem)
Observe that you defective keyboard has bitten you here. If this
method's formal parameter had an uppercase I instead of lower case then
the error "'appItem' is undefined' would not happen as 'appItem' would
then refer to the formal parameter.
> {
> document.write("Testing object passed by reference now <BR
> />");
> // !! This fails to have the object passed in - whats gives
> ?//
> // Gtes appItem is Not defines in javascript console //
> document.write("appItem.appIconElementId : " +
> appItem.appIconElementId);
^^^^^^^
There is your error. It looks like you intended to refer to the method's
parameter but have actually used an Identifier that does not resolve as
a named property of any object on the method's scope chain.
> appItem.isCurrent = true;
> }
The same as above applies to this 'SetCurrentItem' method.
> this.GetCurrentItem = function()
> {
> for(var x=0; x < this.appList.length; x++)
> {
> if(this.appList[x].isCurrent == true)
> {
> return this.appList[x];
> }
> return null;
> }
> }
The same as above applies to this 'GetCurrentItem' method.
> }
<snip>
All of this worthless creation of function object instances with each
creation of an ' AppModel' instance can be avoided by assigning a single
function object instance to named properties of the constructor's
prototype. E.G:-
function AppModel()
{
this.currentItem = null;
this.appList = new Array();
}
AppModel.prototype.Add = function(appItem)
{
...
};
AppModel.prototype.GetAppItemByIconElementId = function(id)
{
...
};
AppModel.prototype.GetAppItemByPanelElementId = function(id)
{
...
};
AppModel.prototype.SetCurrentItem = function(appitem)
{
...
};
AppModel.prototype.GetCurrentItem = function()
{
...
};
Richard.
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