simple javacript coding required

See attached booking form that is part of a drupal application. The user selects an arrival date and then when they click into the departure date field it inserts a date that is 2 days later. A small bit of javascript needs to be added to the javascript validation that already occurs on this page. Add javascript code to ensure the following conditions are met: 1) user cannot select booking dates that are in the past (incl the current day) 2) user cannot select booking dates that are less than 2 days in the future. For example if today is 11 July, they can only select an arrival date of 13 July. Freelancer can make code additions in this file and I can test within Drupal app.