JAVASCRIPT

select2 get selected value

//get all selected select object
$('#select2Id').find(':selected');

//get all selected value 
$("#select2Id").select2("val");

multiple value selected in select2

var selectedValuesTest = ["WY", "AL", "NY"];
$(document).ready(function() {
  $("#e1").select2({
    multiple: true,
  });
  $('#e1').val(selectedValuesTest).trigger('change');
});

select2 multi select get selected value

alert("Selected value is: "+$(".leaderMultiSelctdropdown").select2("val"));

alternatively, if you used a regular selectbox as base, you should be able to
use the normal jquery call, too:

alert("Selected value is: "+$(".leaderMultiSelctdropdown").val());

select2 multiple selected values

in_array($value, $array)