title: Chart.js chart.update() method is not doing anything
body: <p>I am working with Chart.js. I have a chart that can display the data. I also have different datasets that I would like to interchange on a button press. 
  All the datasets are in an array and should just be interchanged with my method. Once I changed all the values, I call the <code>update()</code> method. Nothing happens!</p>
  
  <p>I have checked the content of <code>char.data.datasets.data</code> and it does in fact contain the current data. The only thing is, that Chart.js does not seem to want to update. </p>
  
  <p>What am I missing here? </p>
  
  <p>The function that updates the chart:</p>
  
  <pre><code>let getValues = function(dataset, label)
  {
    return firebase.database().ref("/data/" + dataset).once("value").then(function(snapshot)
    {
      var amazon = snapshot.val().Amazon;
      var google = snapshot.val().Google;
      var facebook = snapshot.val().Facebook;
      var twitter = snapshot.val().Twitter;
  
  
      chart.data.datasets.data = [];
      chart.data.labels = [];
      chart.data.datasets.label = null;
  
      chart.data.datasets.data = [amazon, google, facebook, twitter];
      chart.data.labels = names;
      chart.data.datasets.label = label;
      chart.update();
      console.log(chart.data.datasets.data);
    });
  }
  </code></pre>
  
  <p>If you need any more information please let me know.</p>