How can I change format of jQuery Datepicker date?

When you create a datepicker, you have not mentioned any date format so you just need to mention date format also, while initializing datepicker in any input textbox, so for your above input box, jQuery code will be

$('#datePicker').datepicker({
   dateFormat: 'mm-dd-yy' //your date format
});

For other date formats, you can change jQuery code as per your need

$('#datePicker').datepicker({
   dateFormat: 'dd/mm/yy' //your date format
});

Output:

27/04/2017

Similarly for short  date “d M, y” 

$('#datepicker').datepicker({
    dateFormat: 'd M, y' //output 27 April, 17
});

For showing full date, your date format will be  'DD, d MM, yy'

$('#datepicker').datepicker({
    dateFormat: 'DD, d MM, yy' //Friday, 27 April, 2018
});