Date:<input type="text" id="datepicker">

$(function() {
    $( "#datepicker" ).datepicker({
      dateFormat: 'dd-mm-yy',
      beforeShowDay: checkAvailability
      
      });
      })
       

  function checkAvailability(mydate){
 
   
    if(typeof dates == "undefined"){
   
       dates=[{"dates":"19-09-2019"},{"dates":"20-09-2019"},{"dates":"21-09-2019"},{"dates":"22-09-2019"}];
    }
    var myBadDates = dates;
              
        var $return=true;
        var $returnclass ="available";
        $checkdate = $.datepicker.formatDate('dd-mm-yy', mydate);
        
                                
        for(var x in myBadDates)
         {  
            console.log(x);
                  if(myBadDates[x].dates == $checkdate){
                    $return=false;
                    $returnclass="unavailable";
                  }
           
          
          }                  
          
                            

        return [$return,$returnclass];
  }