Cannot get value from the textbox inside ext.window

[eldhose]

i am placed a asp.net form inside ext.net window content and am using jqery and ajax update panel
my problem is that am not getting the textbox value in javascript
document.getElementById('txtAccountName').value return ""(empty)
if i put like these am getting value
document.getElementById('txtAccountName').children .txtAccountName.value return "abcd"

why these happaned ?..

[eldhose]

can any one tell me how can use direct javascript to get value
instead of using children