Drupal 7 module form_alter to set 2 date fields the same value if one changes

Question

I need help to make a custom module to make 2 date fields in a content type to have always the same values using JavaScript.

I have a content type called interpello . It has 2 date fields (pop-up calendar) named “data inizio” (field_data_inizio) and “data fine” (field_data_fine) in the format “d-m-Y h:m ”. Is there a way (using Ajax or JavaScript) to set the 2 date fields have always the same value, and if “data inizio” changes has to change “data fine” too. Thanks for any answer