<div id="datepicker"></div>

$(document).ready(function () {

        $("#datepicker").datepicker({
            onSelect: function (dateText, inst) {
                var date = $(this).val();
                alert(date);
            }
        });

    });

$(function() {
    $("#datepicker").datepicker();
    $("#datepicker").on("change",function(){
        var selected = $(this).val();
        alert(selected);
    });
});

$(function() {
    $( "#datepicker" ).datepicker({ dateFormat: "yy-mm-dd" });
    $("#datepicker").on("change",function(){
        var selected = $(this).val();
        alert(selected);
    });
});

$(function() {
    $("#datepicker").datepicker({
        dateFormat: "yy-mm-dd",
        onSelect: function(){
        var selected = $(this).val();
        alert(selected);
        }
    });
});

$("#datepicker").datepicker({
     onSelect:function(selectedDate)
     {
          alert(selectedDate);
     }
});

$("#datepicker").datepicker({
     onSelect:function (dateText, inst)
     {
          alert(inst);
     }
});

<div id='QA'></div>
<div id='datepicker'></div>

<script type="text/javascript">
    $(function() {
        $('#datepicker').datepicker({
            clearBtn: true,
            todayHighlight: false,
            multidate: true

        }) .on('changeDate', function(e){
            $('#QA').html(JSON.stringify(e));
        });
    });
    /*
    {
       "type":"changeDate",
       "date":"2015-08-08T07:00:00.000Z",
       "dates":[
         "2015-08-08T07:00:00.000Z"
       ],
       "timeStamp":1438803681861,
       "jQuery21409071635671425611":true,
       "isTrigger":3,
       "namespace":"",
       "namespace_re":null,
       "target":{

       },
       "delegateTarget":{

       },
       "currentTarget":{

       },
       "handleObj":{
         "type":"changeDate",
         "origType":"changeDate",
         "guid":52,
         "namespace":""
       }
    }
    */

</script>

$('.selector').datepicker({
   onSelect: function(dateText, inst) { ... }
})

first = $(".datepicker[name=datepicker1]").datepicker('getDate');
second = $(".datepicker[name=datepicker2]").datepicker('getDate');