ChartJS: Custom tooltip always displaying - charts

Question

Im using ChartJS to create a graph on my website.
Im trying to create a custom tooltip. According to the documentation, this should be easy:
var myPieChart = new Chart(ctx, {
type: 'pie',
data: data,
options: {
tooltips: {
custom: function(tooltip) {
// tooltip will be false if tooltip is not visible or should be hidden
if (!tooltip) {
return;
}
}
}
}
});
My problem is that the tooptip is never false and because of this my custom tooltip is always displayed.
Please see this JSFiddle (line 42 is never executed)
Question: Is it a bug that tooltip is never false, or am I missing something?

Answer 1

The custom tooltip option is used for when you want to create/style your own tooltip using HTLM/CSS outside of the scope of the canvas (and not use the built in tooltips at all).
In order to do this, you must define a place outside of your canvas to contain your tooltip (e.g. a div) and then use that container within your tooltips.custom function.
Here is an example where I used a custom tooltip to display the hovered pie chart section percentage in the middle of the chart. In this example I'm generating my tooltip inside a div with id "chartjs-tooltip". Notice how I interact with this div in my tooltips.custom function to position and change the value.
Also, the correct way to check if the tooltip should be hidden is to check it's opacity. The tooltip object will always exist, but when it should not be visible, the opacity is set to 0.
Chart.defaults.global.tooltips.custom = function(tooltip) {
// Tooltip Element
var tooltipEl = document.getElementById('chartjs-tooltip');
// Hide if no tooltip
if (tooltip.opacity === 0) {
tooltipEl.style.opacity = 0;
return;
}
// Set Text
if (tooltip.body) {
var total = 0;
// get the value of the datapoint
var value = this._data.datasets[tooltip.dataPoints[0].datasetIndex].data[tooltip.dataPoints[0].index].toLocaleString();
// calculate value of all datapoints
this._data.datasets[tooltip.dataPoints[0].datasetIndex].data.forEach(function(e) {
total += e;
});
// calculate percentage and set tooltip value
tooltipEl.innerHTML = '<h1>' + (value / total * 100) + '%</h1>';
}
// calculate position of tooltip
var centerX = (this._chartInstance.chartArea.left + this._chartInstance.chartArea.right) / 2;
var centerY = ((this._chartInstance.chartArea.top + this._chartInstance.chartArea.bottom) / 2);
// Display, position, and set styles for font
tooltipEl.style.opacity = 1;
tooltipEl.style.left = centerX + 'px';
tooltipEl.style.top = centerY + 'px';
tooltipEl.style.fontFamily = tooltip._fontFamily;
tooltipEl.style.fontSize = tooltip.fontSize;
tooltipEl.style.fontStyle = tooltip._fontStyle;
tooltipEl.style.padding = tooltip.yPadding + 'px ' + tooltip.xPadding + 'px';
};
Here is the full codepen example.
I hope that helps clear things up!