title: Ajax post error but errorThrown empty
body: <p>Can someone help me in find what's my error in tihis ajax post request? </p>
  
  <p>This is html</p>
  
  <pre><code>&lt;select onchange="fetch_pro(this.value);"&gt;
      &lt;option&gt;select&lt;/option&gt;
      &lt;option value="1"&gt;option 1&lt;/ option&gt;
      &lt;option value="2"&gt;option 2&lt;/ option&gt;
      &lt;option value="3"&gt;option 3&lt;/ option&gt;
  &lt;/select&gt;
  
  &lt;script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"&gt;&lt;/script&gt;       
  
      &lt;script type="text/javascript"&gt;
          function fetch_pro(val)
          { 
           $.ajax({
           type: 'post',
           url: 'fetch.php',
           data: {
            id_reg:val
           },
           dataType: "json", 
           cache: false,
           success: function (response) {
            alert (response); 
           },
           error: function(XMLHttpRequest, textStatus, errorThrown) { 
              alert("Status: " + textStatus); alert("Error: " + errorThrown);
          } , 
           });
          }   
  &lt;/script&gt; 
  </code></pre>
  
  <p>and this is sample fetch.php</p>
  
  <pre><code>&lt;?php
  echo "ok";
  ?&gt;
  </code></pre>
  
  <p>It return status error but error empty, what's wrong?</p>