Get a value of a field by Javascript.

Dears,

 

I have written a sample Javascript code. The behavior of the sample code is to create a button on the call page. When a user clicks on the button, the sample javascript code will get some values of the call page and create a new record in the CustomObject7 depends on that values.

 

My concern is that when I try to get a value of a field that does not show in the call page, I can’t. Only, I can get the values of the fields that are shown on the call page. For instance, I want to get the contact Id value, but I can’t, because it does not show on the call page and I can’t show it on the call page as well.