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Trevor:
Trevor:
Legend
July 4, 2012
Answered

Get Object Property Elements and Values

  • July 4, 2012
  • 3 replies
  • 1734 views

If I have an object,

myObject = ({a:3, b:5, c:8})

how can I get a list of the elements and their values according to their position

Let's say I want to know what the name of the second element, how can I get the answer "b"?

Also, without knowing the element name how can I get the value of the second element "5" ?

Thanks

Trevor

This topic has been closed for replies.
Correct answer John Hawkinson

This is, of course, a Javascript question, and the answer is not particular to InDesign, though I think you knew that.

The short answer is: You don't. Javascript does not guarantee anything about the positioning of members of an Object.

There is no guarantee that b will remain the second element, and there is no way to get the members of an Object by some kind of index other than their name.

BTW, you write:

myObject = ({a:3, b:5, c:8})

Which is overly complex (extra parens) and missing a line-terminating semicolon. This is better written as:

myObject = {a:3, b:5, c:8};

You can iterate over the names of the keys to myObject, with for (i in myObject) { ... }, but again there are no ordering guarantees. In ExtendScript, you could use myObject.reflect.properties to return the keynames in array form, but you'll get some extra junk and it's not really consider good practice to use the reflection objects in non-debugging code.

If you find yourself wanting to do this, you are probably not using Objects correctly.

Can you tell us more about the problem you are trying to solve, please?

3 replies

Harbs.
Harbs.
Legend
July 4, 2012

John is correct. You cannot guarantee the order of properties in a Javascript object.

John Hawkinson
John HawkinsonCorrect answer
Inspiring
July 4, 2012

This is, of course, a Javascript question, and the answer is not particular to InDesign, though I think you knew that.

The short answer is: You don't. Javascript does not guarantee anything about the positioning of members of an Object.

There is no guarantee that b will remain the second element, and there is no way to get the members of an Object by some kind of index other than their name.

BTW, you write:

myObject = ({a:3, b:5, c:8})

Which is overly complex (extra parens) and missing a line-terminating semicolon. This is better written as:

myObject = {a:3, b:5, c:8};

You can iterate over the names of the keys to myObject, with for (i in myObject) { ... }, but again there are no ordering guarantees. In ExtendScript, you could use myObject.reflect.properties to return the keynames in array form, but you'll get some extra junk and it's not really consider good practice to use the reflection objects in non-debugging code.

If you find yourself wanting to do this, you are probably not using Objects correctly.

Can you tell us more about the problem you are trying to solve, please?

Trevor:
Trevor:Author
Legend
July 4, 2012

John, Uwe and Harbs

Thanks for your responses.

Very Helpful, particularly Uwe's example

I understand that if the properties change then so might the positions but I guess that I am correct that if the properties don't change then the positions won't either.

The truth is I don't necessarily need the positions,

I wanted to be able to get the list of the names and elements.

I also want to be able to delete some of the elements and then compare the remaining properties.

I think I have all the information that I need now.

Harbs.
Harbs.
Legend
July 4, 2012

~ Trevor ~ wrote:

I understand that if the properties change then so might the positions but I guess that I am correct that if the properties don't change then the positions won't either.

No. That's not correct. Different implementations of javascript will give you different results without changing anything. Even if you seem to see consistent results, the results can change at any time.


~ Trevor ~ wrote:

I also want to be able to delete some of the elements and then compare the remaining properties.

delete obj.prop;

Trevor:
Trevor:Author
Legend
July 4, 2012

Just want to add, without using regex's

L
Community Expert
LaubenderCommunity Expert
Community Expert
July 4, 2012

@Trevor – try something like that:

var myObject = new Object({a:3, b:5, c:8});
var position = 2;
var counter = 0;
for(x in myObject){
        ++counter;
        if(counter === position){
            $.writeln(x);
            $.writeln(myObject);
            break;
            };
    };

Uwe

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