What does this this ActionScript syntax mean? ( Syntax for returning Objects Inline )

Question

I am a Java programmer and need to work on a Flex/ActionScript project right now. I got an example of using ITreeDataDesriptor from Flex 3 Cookbook, but there is one line of actionscript code that's hard for me to understand. I appreciate if someone could explain this a little further.

public function getData(node:Object, model:Object=null):Object
    {
        if (node is Office) {
            return {children:{label:node.name, label:node.address}};
        }
    }

The part that I didn't understand was "{children:{label:node.name, label:node.address}}". Office is simply a value object that contains two String properties: name and address.

aaaidan · Accepted Answer · 2008-12-17 03:53:26Z

7

The following return expression (modified from the question) ...

return {children:{label:node.name, body:node.address}}

... is functionally equivalent to this code ...

var obj:Object = new Object();
obj.children = new Object();
obj.children.label = node.name;
obj.children.body = node.address;
return obj;

The anonymous object returned in the question code complicates matters because it defines a property twice. In that case, the first declaration is used, and the subsequent one(s) are ignored. No compile-time or runtime error is thrown.

answered Dec 17, 2008 at 3:53

aaaidan

7,3868 gold badges69 silver badges107 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Luke · Accepted Answer · 2008-12-17 01:50:45Z

1

I think in Java you would call that a map or an associative array. In Javascript and Actionscript you can say this to create an object with certain properties:

var myobject = {
   'prop1': 100,
   'prop2': {
      'a': 1
   }
}

trace( myobject.prop1 );   // 100
trace( myobject.prop2.a );   // 1

In your example it's just returned as a nameless object.

answered Dec 17, 2008 at 1:50

Luke

21.4k39 gold badges124 silver badges180 bronze badges

Comments

Robert Gould · Accepted Answer · 2008-12-17 01:51:42Z

1

return {children:{label:node.name, label:node.address}};

Means you are returning a new Object. The {} are the Object's constructor, and in this case its an Anonymous object.

answered Dec 17, 2008 at 1:51

Robert Gould

70.1k62 gold badges193 silver badges275 bronze badges

Comments

Tong Wang · Accepted Answer · 2008-12-17 02:00:38Z

0

Thank you both for the quick response. So if I understand your explanations correctly, the return statement is returning an anonymous object, and this object has only one property named "children", which is again an associative array - ok, here is the part I don't quite understand still, it seems that both properties in this array are named "label", is this allowed?

answered Dec 17, 2008 at 2:00

Tong Wang

1,6124 gold badges29 silver badges37 bronze badges

5 Comments

Robert Gould Over a year ago

That syntax is probably an ActionScript thing, it won't work as such in ECMA/Javascript. You'd need the "" marks to name your vars. Or it might be a typo in the book's code. Did you try compiling/looking at the included sample code(if there is any)?

aaaidan Over a year ago

Although it's not invalid to declare a property twice in an anonymous object declaration, only the first one is used. So for the example in your question, the label property would have the value of node.name, and the second declaration would be ignored. Stupid, but whatever.

aaaidan Over a year ago

Tong Wang - Also, just a friendly pointer about responses to answers: they should generally be left as comments on the answer itself, rather than as a separate answer.

Tong Wang Over a year ago

I tried the example and it worked fine. One thing I noticed is that the object that has "label" property defined twice is in getData() method, which doesn't seem to be called anywhere in Tree.as (the source of the Tree control), while the other 5 methods of the ITreeDataDescriptor are called.

Tong Wang Over a year ago

Does anyone know what is the purpose of getData()? The doc only says "Gets the data from a node.", which doesn't really help.

Collectives™ on Stack Overflow

What does this this ActionScript syntax mean? ( Syntax for returning Objects Inline )

4 Answers 4

Comments

Comments

Comments

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related