title: ChartJS: Update tooltip
body: <p>I'm having a chart build with ChartJS. I'm including datasets.label in multipleTooltipLabel template and facing an update issue. When changing a datasets.label and running <code>chart.update()</code> the tooltip is not updated. I created a <a href="https://jsfiddle.net/sv760bp5/1/" rel="nofollow">JSFiddle demonstrating the issue</a>.</p>
  
  <p>The code I use to include datasets label in tooltip:</p>
  
  <pre><code>var options = {
    multiTooltipTemplate: "&lt;%=datasetLabel%&gt;: &lt;%= value + ' %' %&gt;"
  };
  </code></pre>
  
  <p>Beside that option I followed <a href="http://www.chartjs.org/docs/#polar-area-chart-example-usage" rel="nofollow">ChartJS usage example</a> for Line charts.</p>
  
  <p>Change label and update chart:</p>
  
  <pre><code>myNewChart.datasets[0].label = 'updated label';
  myNewChart.update();
  </code></pre>
  
  <p>Label shown in tooltip is not updated...</p>
  
  <p>I had a look in ChartJS source code and figured out that <a href="https://github.com/nnnick/Chart.js/blob/3f2119526d929ea22f8c971c47a242b4a958cdda/Chart.js#L1003-L1144" rel="nofollow"><code>showTooltip</code> function</a> is called with a <code>ChartElements</code> array which was not updated.</p>
  
  <p>Update: I might cached the issue. <code>label</code> of <code>dataset</code> is <a href="https://github.com/nnnick/Chart.js/blob/3f2119526d929ea22f8c971c47a242b4a958cdda/Chart.js#L2369" rel="nofollow">set on each <code>point</code> element</a> and not updated if it changes. <code>showTooltip</code> used this "cached" dataset label when drawing a tooltip. Perhaps this should not be a question on StackOverflow but a bug report for ChartJS.</p>