#ツールチップ

const chart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        plugins: {
            tooltip: {
                callbacks: {
                    label: function(context) {
                        let label = context.dataset.label || '';
                        if (label) {
                            label += ': ';
                        }
                        if (context.parsed.y !== null) {
                            label += new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' }).format(context.parsed.y);
                        }
                        return label;
                    }
                }
            }
        }
    }
});

const chart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        plugins: {
            tooltip: {
                callbacks: {
                    labelColor: function(context) {
                        return {
                            borderColor: 'rgb(0, 0, 255)',
                            backgroundColor: 'rgb(255, 0, 0)',
                            borderWidth: 2,
                            borderDash: [2, 2],
                            borderRadius: 2,
                        };
                    },
                    labelTextColor: function(context) {
                        return '#543453';
                    }
                }
            }
        }
    }
});

const chart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        plugins: {
            tooltip: {
                usePointStyle: true,
                callbacks: {
                    labelPointStyle: function(context) {
                        return {
                            pointStyle: 'triangle',
                            rotation: 0
                        };
                    }
                }
            }
        }
    }
});

{
    // The chart the tooltip is being shown on
    chart: Chart
    // Label for the tooltip
    label: string,
    // Parsed data values for the given `dataIndex` and `datasetIndex`
    parsed: object,
    // Raw data values for the given `dataIndex` and `datasetIndex`
    raw: object,
    // Formatted value for the tooltip
    formattedValue: string,
    // The dataset the item comes from
    dataset: object
    // Index of the dataset the item comes from
    datasetIndex: number,
    // Index of this data item in the dataset
    dataIndex: number,
    // The chart element (point, arc, bar, etc.) for this tooltip item
    element: Element,
}

const myPieChart = new Chart(ctx, {
    type: 'pie',
    data: data,
    options: {
        plugins: {
            tooltip: {
                // Disable the on-canvas tooltip
                enabled: false,
                external: function(context) {
                    // Tooltip Element
                    let 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
                    const tooltipModel = context.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) {
                        const titleLines = tooltipModel.title || [];
                        const bodyLines = tooltipModel.body.map(getBody);
                        let innerHtml = '<thead>';
                        titleLines.forEach(function(title) {
                            innerHtml += '<tr><th>' + title + '</th></tr>';
                        });
                        innerHtml += '</thead><tbody>';
                        bodyLines.forEach(function(body, i) {
                            const colors = tooltipModel.labelColors[i];
                            let style = 'background:' + colors.backgroundColor;
                            style += '; border-color:' + colors.borderColor;
                            style += '; border-width: 2px';
                            const span = '<span style="' + style + '">' + body + '</span>';
                            innerHtml += '<tr><td>' + span + '</td></tr>';
                        });
                        innerHtml += '</tbody>';
                        let tableRoot = tooltipEl.querySelector('table');
                        tableRoot.innerHTML = innerHtml;
                    }
                    const position = context.chart.canvas.getBoundingClientRect();
                    const bodyFont = Chart.helpers.toFont(tooltipModel.options.bodyFont);
                    // 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.font = bodyFont.string;
                    tooltipEl.style.padding = tooltipModel.padding + 'px ' + tooltipModel.padding + 'px';
                    tooltipEl.style.pointerEvents = 'none';
                }
            }
        }
    }
});

{
    chart: Chart,
    // The items that we are rendering in the tooltip. See Tooltip Item Interface section
    dataPoints: TooltipItem[],
    // Positioning
    xAlign: string,
    yAlign: string,
    // X and Y properties are the top left of the tooltip
    x: number,
    y: number,
    width: number,
    height: number,
    // Where the tooltip points to
    caretX: number,
    caretY: number,
    // Body
    // The body lines that need to be rendered
    // Each object contains 3 parameters
    // before: string[] // lines of text before the line with the color square
    // lines: string[], // lines of text to render as the main item with color square
    // after: string[], // lines of text to render after the main lines
    body: object[],
    // lines of text that appear after the title but before the body
    beforeBody: string[],
    // line of text that appear after the body and before the footer
    afterBody: string[],
    // Title
    // lines of text that form the title
    title: string[],
    // Footer
    // lines of text that form the footer
    footer: string[],
    // style to render for each item in body[]. This is the style of the squares in the tooltip
    labelColors: TooltipLabelStyle[],
    labelTextColors: Color[],
    labelPointStyles: { pointStyle: PointStyle; rotation: number }[],
    // 0 opacity is a hidden tooltip
    opacity: number,
    // tooltip options
    options: Object
}

import { Tooltip } from 'chart.js';
/**
 * Custom positioner
 * @function Tooltip.positioners.myCustomPositioner
 * @param elements {Chart.Element[]} the tooltip elements
 * @param eventPosition {Point} the position of the event in canvas coordinates
 * @returns {TooltipPosition} the tooltip position
 */
Tooltip.positioners.myCustomPositioner = function(elements, eventPosition) {
    // A reference to the tooltip model
    const tooltip = this;
    /* ... */
    return {
        x: 0,
        y: 0
        // You may also include xAlign and yAlign to override those tooltip options.
    };
};
// Then, to use it...
new Chart.js(ctx, {
    data,
    options: {
        plugins: {
            tooltip: {
                position: 'myCustomPositioner'
            }
        }
    }
})