title: Chart js update multiple charts
body: <p>I've seen many tutorials on how to add data in chart.js, but it's all for a single chart.</p>
  
  <p>I use chartjs to create multiple charts (each one has its own canvas with an unique ID).
  For example: Chart 1 is in a canvas with id="c1" and chart 2 is in a canvas with id="c2". How can I select chart 1 and add new data?</p>