How would I link a ChartJS doughnut chart to completed lists that contain a checklist?

How would I go about linking a ChartJS doughnut chart to several tasks when they are checked off as "completed"?

Think of a 5 lists in Trello with items checked off within each one. And once the overall progress bar reaches 100% on each of the 5 lists, the ChartJS chart increases by 20% for each one. Acting almost an overall Progress Gauge.

I'm guessing that I would need some type of conditional statement within the JS. Thanks