Hiding Fields

Hi Guys/Gals

I am currently working on a custom record form. I have a number of fields that I need to be able to hide when a certain value is selected from a drop down.

I have seen the following snippet of code on the forums already:

         form.getField('custbody_optional_field').setDisplayType('hidden') 

But form is always undefined, even though i am passing the default form parameters into the function.

My code is currently running from the field change function.

My only alternative is to have a number of preset form layouts with the correct fields hidden/shown, and change this when the value is selected, the only problem is that I need some values passing from the original form to the new form, and whenever I change the form it looses all the original values.