Legend

The chart legend displays data about the datasets that are appearing on the chart.

Configuration options

Namespace: options.plugins.legend, the global options for the chart legend is defined in Chart.defaults.plugins.legend.

Position

Position of the legend. Options are:

• 'top'
• 'left'
• 'bottom'
• 'right'
• 'chartArea'

When using the 'chartArea' option the legend position is at the moment not configurable, it will always be on the left side of the chart in the middle.

Align

Alignment of the legend. Options are:

• 'start'
• 'center'
• 'end'

Defaults to 'center' for unrecognized values.

Legend Label Configuration

Namespace: options.plugins.legend.labels

Legend Title Configuration

Namespace: options.plugins.legend.title

Legend Item Interface

Items passed to the legend onClick function are the ones returned from labels.generateLabels. These items must implement the following interface.

{
    // Label that will be displayed
    text: string,
    // Border radius of the legend item.
    // Introduced in 3.1.0
    borderRadius?: number | BorderRadius,
    // Index of the associated dataset
    datasetIndex: number,
    // Fill style of the legend box
    fillStyle: Color,
    // Text color
    fontColor: Color,
    // If true, this item represents a hidden dataset. Label will be rendered with a strike-through effect
    hidden: boolean,
    // For box border. See https://developer.mozilla.org/en/docs/Web/API/CanvasRenderingContext2D/lineCap
    lineCap: string,
    // For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setLineDash
    lineDash: number[],
    // For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineDashOffset
    lineDashOffset: number,
    // For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineJoin
    lineJoin: string,
    // Width of box border
    lineWidth: number,
    // Stroke style of the legend box
    strokeStyle: Color,
    // Point style of the legend box (only used if usePointStyle is true)
    pointStyle: string | Image,
    // Rotation of the point in degrees (only used if usePointStyle is true)
    rotation: number
}

Example

The following example will create a chart with the legend enabled and turn all of the text red in color.

var chart = new Chart(ctx, {
    type: 'bar',
    data: data,
    options: {
        plugins: {
            legend: {
                display: true,
                labels: {
                    color: 'rgb(255, 99, 132)'
                }
            }
        }
    }
});

Custom On Click Actions

It can be common to want to trigger different behaviour when clicking an item in the legend. This can be easily achieved using a callback in the config object.

The default legend click handler is:

function(e, legendItem, legend) {
    const index = legendItem.datasetIndex;
    const ci = legend.chart;
    if (ci.isDatasetVisible(index)) {
        ci.hide(index);
        legendItem.hidden = true;
    } else {
        ci.show(index);
        legendItem.hidden = false;
    }
}

Lets say we wanted instead to link the display of the first two datasets. We could change the click handler accordingly.

var defaultLegendClickHandler = Chart.defaults.plugins.legend.onClick;
var newLegendClickHandler = function (e, legendItem, legend) {
    var index = legendItem.datasetIndex;
    if (index > 1) {
        // Do the original logic
        defaultLegendClickHandler(e, legendItem, legend);
    } else {
        let ci = legend.chart;
        [
            ci.getDatasetMeta(0),
            ci.getDatasetMeta(1)
        ].forEach(function(meta) {
            meta.hidden = meta.hidden === null ? !ci.data.datasets[index].hidden : null;
        });
        ci.update();
    }
};
var chart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        plugins: {
            legend: {
                onClick: newLegendClickHandler
            }
        }
    }
});

Now when you click the legend in this chart, the visibility of the first two datasets will be linked together.