I'm attaching an event listener to a chart in a richlet using a piece of code like the following:

chart.addEventListener(10, Events.ON_CLICK, (Event event) -> {
   //code to execute...
});

On the client, when the user clicks anywhere on the chart, the event listener is never called. However, the browser console displays the following error:

TypeError: j.mouseData is not a function

The root cause of the error can be traced back to Charts.js, and more specifically to the following call when handling 'onClick' events:

zk.copy(event.mouseData(), {
    xAxis: event.xAxis[0].value,
   yAxis: event.yAxis[0].value
})

Replacing that call with "null" makes the client-side error go away and subsequently allows the server-side event listener to be called.