ChartsJS Annotations Plugin - Can you create a tooltip to accompany an annotation?

Question

im trying to figure out how I can add a tooltip when I hover/mouseover the vertical line annotation I've drawn:

annotation: {
   annotations: [{
      "drawTime": "afterDatasetsDraw",
      "type": "line",
      "mode": "vertical",
      "scaleID": "x-axis-0",
      "value": "2020-04-01 12:20:27.709523",
      "borderWidth": 2,
      "borderColor": "red",
      "label": {
        "content": "Example Content",
        "enabled": true,
        "position": "top"
      },
      onMouseover: function(e) {
        console.log("I AM GETTING CALLED!");
      },
   },

Can anybody explain how this can be done?

Answer 1

You can use a label for the annotation whose display is changed when the mouse enters and leaves (see Events configuration).

annotation: {
    annotations: [{
        type: 'line',
        borderWidth: 2,
        xMin: someX,
        xMax: someX, // xMin = xMax for vertical line
        label: {
            display: false,
            backgroundColor: 'green',
            drawTime: 'afterDatasetsDraw',
            content: 'Some content for tooltip'
        },
        enter({ element }, event) {
            element.label.options.display = true;
            return true; // force update
        },
        leave({ element }, event) {
            element.label.options.display = false;
            return true;
        }
    }]
}

See the Label visibility example in the chartjs-plugin-annotation documentation.

Answer 2

Not directly answering your question, but you can modify the chart and annotations in any way you prefer (in ChartJS v3) by accessing the context chart and element (docs)

I used this to change style of annotation on hover (in TypeScript):

enter: (context) => {
    const id = context.element.options.id!;
    ((context.chart.options.plugins!.annotation!.annotations as any)[id] as AnnotationOptions).borderColor = 'blue';
    context.chart.canvas.style.cursor = 'pointer';
    context.chart.update();
},
leave: (context) => {
    const id = context.element.options.id!;
    ((context.chart.options.plugins!.annotation!.annotations as any)[id] as AnnotationOptions).borderColor = 'rgb(255, 99, 132)';
    context.chart.canvas.style.cursor = 'default';
    context.chart.update();
},