Ajax success function not processing of "document.getElementById" function

Next is from header:

 Select project from the list: <select id="selectProjectID" onfocus="onFocusSelectProject()">
                   </select></br></br>

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And next is ajax call.

  function getLastOpenedProject(){  //_____________getLastOpenedProject(){ 
  $.ajax({
  method:"POST",
  url: '/wp-content/themes/net4/PgetJson.php',
  data:  {
      "getLastOpenedProject":1,
       "weGotTheuser":weGotTheuser
   datatype: "text",
    success: function(strdate){
         var selectProject3 = document.getElementById("selectProjectID");
      selectProject3.value=strdate;
      alert(strdate);
     }
  }); 
 }

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"Alert" gives me right answer from DB.  What is then wrong in my code? I don't get anything in "select " element.