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$(document).ready(function () {

  var select2 = $('select');

  var data = [
      { id: 0, text: 'enhancement' }, 
      { id: 1, text: 'bug' }, 
      { id: 2, text: 'duplicate' }, 
      { id: 3, text: 'invalid' }, 
      { id: 4, text: 'wontfix' }
  ];

  select2.select2({
      placeholder: 'Select a state',
      data: data,
      minimumResultsForSearch: Infinity //Hiding the search box
  });

  $("#readValue").click(function (e) {
      alert("value is " + $('select').val());
  })
  $("#setBug").click(function () {
      select2.val([1,3,4]).trigger('change');//set all option in one time, failure in One by one.
  })
  $("#setEmpty").click(function () {
      select2.val(null).trigger('change');
  })
  
  
});
<select name="status" multiple="multiple" style="width: 200px;">
</select>

<br>
<br>
<button id="readValue">Read Value</button>
<button id="setBug">Set "bug invalid wontfix"</button>
<button id="setEmpty">Clear</button>

              

External resources loaded into this fiddle: