[JS, CS4] TextFrame.extractLabel() cannot work with instances of this class

Question

I have script, which has been working fine in CS3. In CS4 ( app.version = 6.0.1.532 ) however, I get an error using extractLabel, after reading out a couple of other properties from a textframe:
frameObject.extractLabel('name')
Error: TextFrame.extractLabel() cannot work with instances of this class
Up until reading one of the "normal" properties, such as (frameObject.)contents I can call the frameObject.extractLabel('name') without errors, but after "looking at" (by assigning to a variable in code, or by getting the value in the javascript console), the contents propery (or as it seems any normal property) the extractLabel method results in the error above.
It seems to work to move all of the frameObject.extractLabel calls to the beginning of the function, but I don't think I should need to do that.
It might very well be the case that the label read by extractLabel has no contents, and has never been assigned. Is there a change in behaviour from CS3 in that sentence? If so, and if thats the reason for the error, is there then a way to determine whether the label has ever been assigned?
Is this error familiar to anyone else?
Best regards,
Andreas

Answer 1

Hi Andreas,
Interesting problem!
Your problems are caused by some peculiarities of itemByID. itemByID doesn't cast the object type properly. Dirk wrote about some aspects of this some time ago. If the scripting engine was strongly typed, this issue would probably be impossible but that would make scripting a lot more of an elitist activity!
Your problem is that the object type is PageItem and you are accessing a TextFrame property (content). This seems to throw the object type for a loop.
Using getElements() causes the scripting engine to rebuild the reference to the object correctly.
Take a look at this code, which illustrates the issue quite well...
var myDocument = app.documents.add();
myDocument = app.activeDocument;
myDocument.viewPreferences.horizontalMeasurementUnits = MeasurementUnits.points;
myDocument.viewPreferences.verticalMeasurementUnits = MeasurementUnits.points;
var myTextFrame = myDocument.pages.item(0).textFrames.add({geometricBounds:[72, 72, 144, 288], contents:"test"});
var myId = myTextFrame.id;
var pgItm = myDocument.pageItems.itemByID(myId);
alert(pgItm instanceof PageItem);
alert(pgItm instanceof TextFrame);
var thisBounds = pgItm.geometricBounds;
var x = pgItm.extractLabel('mandatory');
var pgItm = myDocument.textFrames.itemByID(myId);
alert(pgItm instanceof PageItem);
alert(pgItm instanceof TextFrame);
var thisName = pgItm.extractLabel('name');
var thisContents = pgItm.contents;
var x = pgItm.extractLabel('mandatory');
Harbs