title: Highcharts Error: TypeError: undefined is not an object (evaluating 'chart.yAxis')
body: <p>I'm trying to update a chart after I receive success from an ajax call, but I'm getting this error:  <code>TypeError: undefined is not an object (evaluating 'chart.yAxis')</code>. I'm pretty sure I'm calling the update method correctly. Any ideas? Is the scope of chart affected? it is defined when I check it. </p>
  
  <pre><code>var chart = .... chart ....
  $('button#glucose_goals').click(function() {
      $.ajax({
          url:'glucose/goals',
          type: 'POST',
          data: $('form#glucose_boundary_form').serialize(),
          success: function(data) {
              chart.yAxis[0].update({ plotBands: [] });
              chart.redraw();
          }
      });
  });
  </code></pre>