title: preventDefault() in AJAX doesn't work
body: <p>Why doesn't <code>event.preventDefault();</code> work in this AJAX-setting?</p>
  
  <pre><code>$( "#formID" ).submit(function( event ) {
      $.ajax({
          url: "ajax.php",
          type: "GET",
          data: { 'data': 'anything' },
          dataType: "json"
      })
      .done(function( json ) {
          if (!json.result) { 
              event.preventDefault();
          }
      });
  });
  </code></pre>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>On submitting a form I want to check via Ajax if a condition is true or false.
  Depending on that the submit should be prevented (if result of the AJAX call is false).</p>
  
  <p>Is this possible? </p>