get end date of availibility in calendar

[azzeddine05]

hello i'm using a calendar for project availibility, and my data geted from database is colored by unavailable and i get start date correctly using this code

     $('.basic').calendar({
           unavailable: availabilities,
            onSelectDate: function (date, month, year) {
             const adId = $('#add-container').data('adId');
             var start_date = [year,month >= 10 ? month : '0'+month,date >= 10 ? date : 
            '0'+date].join('- 
       ');

but now i want also get date end of interval please any help