title: Date Range Picker - IsInvalidDate / IsCustomDate
body: <p>I currently am using DateRangePicker by <a href="http://www.daterangepicker.com" rel="nofollow noreferrer">http://www.daterangepicker.com</a> and have the following code for my project : </p>
  
  <pre><code>&lt;form name="calform" action="res_info.php"&gt;
  &lt;div&gt;Checkout&lt;input type="text" name="checkout"/&gt;&lt;/div&gt;
  &lt;script type="text/javascript"&gt;
  
  $(function() {
  isInvalidDate: function(date) {
      if (date.format('YYYY-M-D') == '2017-11-12') {
          return true; 
      }
  }
      $('input[name="checkout"]').daterangepicker({
          singleDatePicker: true,
          "locale": {
          format: 'YYYY-M-D'
    }
      }, 
      function(start, end, label) {
          var years = moment().diff(start, 'years');
      });
      $('.calendar.right').show();
  });
  &lt;/script&gt;
     &lt;div&gt; &lt;input type="submit" value="Submit"&gt;&lt;/div&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>But for some reason , <code>isInvalidDate</code> function doesn't work at all. Please Help.</p>