Documentation Is:

• Missing or needed
• Confusing
• Not Sure?

The problem

When you want to alter the default tooltip for a chart, it is not clear how to do it:
https://www.chartjs.org/docs/latest/configuration/tooltip.html#label-callback

I had to dig in the source code of chart.js to see what the default callback looked like.

My proposal for Changes

Replace the example in the documentation with an example that actually works:

Example

var chart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        tooltips: {
            callbacks: {
                label: function(tooltipItem, data) {
                  var dataLabel = data.labels[tooltipItem.index];
                  var value = ': ' + data.datasets[tooltipItem.datasetIndex].data[tooltipItem.index];

                  if (helpers$1.isArray(dataLabel)) {
                    // show value on first line of multiline label
                    // need to clone because we are changing the value
                    dataLabel = dataLabel.slice();
                    dataLabel[0] += value;
                  } else {
                    dataLabel += value;
                  }

                  return dataLabel;
                }
            }
        }
    }
});