Chartjs-In ChartJS how do you format the hover over label in a time series?

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I found this approach:

External (Custom) Tooltips
Custom tooltips allow you to hook into the tooltip rendering process so that you can render the tooltip in your own custom way. Generally this is used to create an HTML tooltip instead of an oncanvas one. You can enable custom tooltips in the global or chart configuration like so:

var myPieChart = new Chart(ctx, {
type: ‘pie’,
data: data,
options: {
tooltips: {
// Disable the on-canvas tooltip
enabled: false,

        custom: function(tooltipModel) {
            // Tooltip Element
            var tooltipEl = document.getElementById('chartjs-tooltip');

            // Create element on first render
            if (!tooltipEl) {
                tooltipEl = document.createElement('div');
                tooltipEl.id = 'chartjs-tooltip';
                tooltipEl.innerHTML = '<table></table>';
                document.body.appendChild(tooltipEl);
            }

            // Hide if no tooltip
            if (tooltipModel.opacity === 0) {
                tooltipEl.style.opacity = 0;
                return;
            }

            // Set caret Position
            tooltipEl.classList.remove('above', 'below', 'no-transform');
            if (tooltipModel.yAlign) {
                tooltipEl.classList.add(tooltipModel.yAlign);
            } else {
                tooltipEl.classList.add('no-transform');
            }

            function getBody(bodyItem) {
                return bodyItem.lines;
            }

            // Set Text
            if (tooltipModel.body) {
                var titleLines = tooltipModel.title || [];
                var bodyLines = tooltipModel.body.map(getBody);

                var innerHtml = '<thead>';

                titleLines.forEach(function(title) {
                    innerHtml += '<tr><th>' + title + '</th></tr>';
                });
                innerHtml += '</thead><tbody>';

                bodyLines.forEach(function(body, i) {
                    var colors = tooltipModel.labelColors[i];
                    var style = 'background:' + colors.backgroundColor;
                    style += '; border-color:' + colors.borderColor;
                    style += '; border-width: 2px';
                    var span = '<span style="' + style + '"></span>';
                    innerHtml += '<tr><td>' + span + body + '</td></tr>';
                });
                innerHtml += '</tbody>';

                var tableRoot = tooltipEl.querySelector('table');
                tableRoot.innerHTML = innerHtml;
            }

            // `this` will be the overall tooltip
            var position = this._chart.canvas.getBoundingClientRect();

            // Display, position, and set styles for font
            tooltipEl.style.opacity = 1;
            tooltipEl.style.position = 'absolute';
            tooltipEl.style.left = position.left + window.pageXOffset + tooltipModel.caretX + 'px';
            tooltipEl.style.top = position.top + window.pageYOffset + tooltipModel.caretY + 'px';
            tooltipEl.style.fontFamily = tooltipModel._bodyFontFamily;
            tooltipEl.style.fontSize = tooltipModel.bodyFontSize + 'px';
            tooltipEl.style.fontStyle = tooltipModel._bodyFontStyle;
            tooltipEl.style.padding = tooltipModel.yPadding + 'px ' + tooltipModel.xPadding + 'px';
            tooltipEl.style.pointerEvents = 'none';
        }
    }
}

});

See here

https://www.chartjs.org/docs/latest/configuration/tooltip.html#tooltip-configuration

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