Iterating through object collections

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Mark Rae - 07 Aug 2004 09:40 GMT

Hi,

Is there any way in JavaScript to iterate through an object's properties to
interrogate their values? I'm thinking specifically of the navigator object,
the screen object, the window object and the document object. Something
like:

foreach(obj in screen.properties)
{
document.write(obj.name + " = " + obj.value)
}

Any assistance gratefully received.

Mark

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Martin Honnen - 07 Aug 2004 13:53 GMT

> Is there any way in JavaScript to iterate through an object's properties to
> interrogate their values? I'm thinking specifically of the navigator object,
[quoted text clipped - 5 lines]
> document.write(obj.name + " = " + obj.value)
> }

for (var property in window.screen) {
document.write('<p>' + property + ': ' + window.screen[property] +
'<\/p>');
}

Signature

Martin Honnen
http://JavaScript.FAQTs.com/

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Mark Rae - 07 Aug 2004 15:18 GMT

> for (var property in window.screen) {
> document.write('<p>' + property + ': ' + window.screen[property] +
> '<\/p>');
> }

Excellent! Thanks.

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Mark Rae - 07 Aug 2004 16:12 GMT

> for (var property in window.screen) {
> document.write('<p>' + property + ': ' + window.screen[property] +

'<\/p>');

> }

Actually, when I came to try this, I couldn't get it to work. I replaced
"for" with "foreach", but that didn't help... :-(

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Martin Honnen - 07 Aug 2004 16:55 GMT

>> for (var property in window.screen) {
>> document.write('<p>' + property + ': ' + window.screen[property] +
[quoted text clipped - 4 lines]
>
> Actually, when I came to try this, I couldn't get it to work.

The code is correct, if you try that with Netscape for instance it shows
you properties that you expect.
The problem with
for (var property in object)
is that it enumerates all properties of the object that are _marked as
being enumerable_ and there is no standard for screen specifying whether
its properties should be marked as being enumerable. Thus if you run the
code with IE/Win for instance and nothing shows up then it is because
the IE implementors have decided to mark the properties of screen as
being not enumerable.

There is nothing you can do about that with your code, but of course
IE's object model is well documented so look into the SDK documentation
first for the properties it defines for an object.

Signature

Martin Honnen
http://JavaScript.FAQTs.com/

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Mark Rae - 07 Aug 2004 18:13 GMT

> There is nothing you can do about that with your code, but of course
> IE's object model is well documented so look into the SDK documentation
> first for the properties it defines for an object.

OK - thanks.

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Iterating through object collections

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