🚀 go-pugleaf

Fred,

Right. It was that realization that had it making sense for me, once I'd thought it through.

I wonder which is quicker:

for (var j in myArray)

for (var j = 0; myArray.length > j; j++)

I appreciate that these aren't necessarily equivalent, but every time I use the latter, I surely could have used the former.

Dave

There is a difference between the two. In the second example below, i is a string, not an int. (put a debugger statement in there and do typeof( i ); in the console to prove it). In the second example we're asking for the array index of:
"01", "11", "12"...

And they're all undefined.

I NEVER use the for( var i in array ) syntax for that reason. If you do introduce a bug there, it's one of those bugs that your eye doesn't catch, and takes forever to find.

Bob

var array = [0,1,2,3,4,5,6,7,8,9];

for ( var i = 0; i < array.length - 1; i++ ) {
	$.writeln( array[ i + 1 ] );
}

for ( var i in array ) {
	$.writeln( array[ i + 1 ] );
}

But why doesn't something like this work?

Isn't myDoc.characterStyles an array?

myDoc = app.activeDocument;
for (j in myDoc.characterStyles)
   alert(myDoc.characterStyles[j].name)

You could do this:

for ( var i in array ) {
	$.writeln( array[ Number(i) + 1 ] );
}

Ah, thanks Bob.

Dave

Exactly, Fred. That's why I never use the var i in array syntax. There's just too many possibilities for subtle errors.

Bob

 > Isn't myDoc.characterStyles an array?

There are 'Collection' objects in Adobe/JS-land that look kinda like Arrays but 
really aren't. It would have been very nice if they would have made these 
collection objects proper subclasses of Array.

I see, so collections don't support the for/in loop as arrays do.

Is there anything else arrays support that collections don't?

Because collections are objects, they do support for/in loops, but the results aren't very useful:

myDocs = app.documents; 
for (j in myDocs) { 
   $.writeln(j); 
}

produces:

length 
Execution finished.

Which indicates that a collection has just one (visible) property named length.

Dave

xbytor wrote: "There are 'Collection' objects in Adobe/JS-land that look kinda like Arrays but really aren't. It would have been very nice if they would have made these collection objects proper subclasses of Array."

That won't work for all of the languages we support. In VBScript, for example, these collections give us capabilities that we would not otherwise have (ItemByName, ItemByRange, etc.). While we could extend Array in JavaScript, we can't do that in the other languages (or, at least, we can't do so given our current process). There are a lot of things that our collections support that arrays don't (except in AppleScript, where arrays and collections work about the same way--in fact, our collections are based on the AppleScript model).

Our "one size fits all" approach does sometimes mean that we can't take advantage of all of the features of a specific language, but it's better than the alternatives--hand coding for each language you want to support (look at some of the other CS applications, which have different DOMs for differing languages), or limiting scripting to a single language.

This is also why I always use the collection.item(index) form when working with these collections and the array[index] form for arrays. This reminder makes it much easier for me when I'm updating scripts.

Thanks,

Ole

It makes sense, because an array is an object and the properties of the 
array are the index number of the array element.

Try this:

var myArray = new Array(50)
myArray[25] = 3
for (j in myArray) {
   $.writeln(j);
}

It seems that myDoc.characterStyles is a regular object with a length 
property added to it, not an actual array.

Another major difference between the for/in and traditional loops is 
that the for/in loop will not loop through the full length of the array 
if it has undefined items whereas the traditional for loop will.

For example:

myDoc = app.activeDocument;
myArray = new Array(myDoc.characterStyles.length)
myArray[3] = 4;
for (j in myArray)
$.writeln(j)

Will only loop once despite the fact that there may be more than one 
character style in the document.