title: responseText is empty, but shows on console?
body: <p>This is probably a stupid error, but I'm using JQuery ajax against PHP backend, and I would like the PHP script to post progress back to the webpage.</p>
  
  <p>It looks to be working fine, but I can't get the contents of e.target.responseText. </p>
  
  <p>If i do console.log(e.target), I get the XMLHttpRequest object in the console. And I can see 
  responseText: "1 av 1500 linjer"</p>
  
  <p>But if I do console.log(e.target.responseText) it is empty.</p>
  
  <p>Have I lost my mind?</p>
  
  <p>This is my function:</p>
  
  <pre><code>$.ajax(
      {
          type: "POST",
          url: "modEcs/ajax/ecs.php?a=analyseExcel",
          processData: false,
          contentType: false,
          xhrFields: 
          {
          onprogress: function(e) 
          {               
              console.log(e.target);
              console.log(e.target.responseText);  
              }
          },
          success: function(data) 
          {
  
           },
           error: function (xhr, ajaxOptions, thrownError) { alert(xhr.statusText); }
      });
  </code></pre>
  
  <p>Data in console:</p>
  
  <pre><code>XMLHttpRequest
  onabort: null
  onerror: null
  onload: null
  onloadend: null
  onloadstart: null
  onprogress: function(e)
  onreadystatechange: null
  ontimeout: null
  readyState: 4
  response: "1 av 1500 linjer"
  responseText: "1 av 1500 linjer"
  responseType: ""
  responseURL: "xxx"
  responseXML: null
  status: 200
  statusText: "OK"
  timeout: 0
  upload: XMLHttpRequestUpload {onloadstart: null, onprogress: null, onabort: null, onerror: null, onload: null, …}
  withCredentials: false
  XMLHttpRequest-prototype
  </code></pre>