Getting Property of DIV from Javascript

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ASP.NET

Javascript

I use following javascript code

var leftCol = window.document.getElementById('leftcol');
var hleftCol = leftCol.offsetHeight;

leftCol is id of a div. I use CollapsiblePanelExtender in the div. I am not getting the same result from the above code. some time hleftCol is expanded height and sometime it is collapsed height although the state of CollapsiblePanelExtender remain same.

could you please help me so that i can get uniform result for each refresh of page.

UPDATE:
OP resolved the issue by himself.