jsf dropdown strange behaviour

[bitostef1]

Hello

i'm extending a java web application which uses extjs and jsf 1.1.
Today has happened a strage behaviuor with a dropdown

in a js file i have this piece of code :

var Obj = document.getElementById('dropDown1');
mittente=Obj.value;

then i use this value as parameter to call another page

i have set the label property of the dropdown (a web.ui.component.dropDown) and the above commands has started to return undefined

Does anybody has any idea why and if it's due to java or javascript
Thanks in advance
S.