title: How to combine two javascript FormData objects
body: <p>I need to combine two FormData objects and post them using XMLHttpRequest. One of the forms contains file input.  </p>
  
  <pre><code>var formData = new FormData(document.forms.namedItem('form-ship'));
  var poData = new FormData(document.forms.namedItem('po-form'));
  
  // Combine them
  var fData = $.extend(true, formData, poData);
  </code></pre>
  
  <p>It doesn't work when I use <code>$.extend</code> or if I use <code>serialize()</code> to combine the form that doesn't have file input. Any idea how to do this?</p>