JavaScript for disabling htmlb elements

Hello,

in my bsp application i want to change the attribute disabled of htmlb:inputfields and htmlb:dropdownlistbox. I used following javascript:

document.getElementById('controllerID_inputfieldID').disabled = 'true';
document.getElementById('controllerID_inputfieldID').disabled = '';

This isn't work right, because the disabled is displayed other than I set disabled in the htmlb tag (<htmlb:inputField id = "inputfieldID" disabled = "true") and I can choice a element in the dropdownlist.

What is the correct javascript function for disabling htmlb elements?

Tina