React ChartsCrosshairs
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Crosshairs show a reference line on the chart, along with the corresponding axis value at a specific position.

When hovering over the chart, the crosshairs can either follow the mouse pointer position or snap to the highlighted item's position to display the axis value at that specific point.

Enabling Crosshairs

To enable the crosshair feature for a given axis, use the crosshair property on the axes options object as shown below:

axes: [
    {
        type: 'number',
        position: 'left',
        crosshair: {
            enabled: true,
        },
    },
],

Snap

By default, the crosshair will snap to the position of the highlighted node.

This default behaviour can be modified by using the crosshair snap option. When snap is false, the crosshair will follow the mouse pointer rather than snapping to the highlighted item.

axes: [
    {
        type: 'number',
        position: 'bottom',
        crosshair: {
            snap: false,
        },
    },
],

Styles

Crosshair styles such as stroke, strokeWidth and lineDash are customisable via AgCrosshairOptions.

crosshair: {
    stroke: '#7290C4',
    strokeWidth: 2,
    lineDash: [5, 10],
},

Label

The crosshair label will be displayed along the axis by default. The label can be removed via the crosshair label option as shown in the code snippet below:

crosshair: {
    label: {
        enabled: false, // removes crosshair label
    },
},

Label Position

The label position relative to the crosshair can be modified using the xOffset and yOffset properties in crosshair.label options as shown below:

crosshair: {
    label: {
        xOffset: 20, // positions label 20px to the right of the start of the crosshair line
        yOffset: 20, // positions label 20px down from the start of the crosshair line
    },
},

Label Format

The crosshair.label.format property can be used to format the crosshair label.

If a format string is not provided, the axis.label.format string will be used.

If neither is present, default formatting will be used: one granularity above axis tick fraction digits for number axes and no formatting for category and time axes.

The example below demonstrates this behaviour.

Notice how when you click on one of the buttons in the example to change the provided configuration, the crosshair label format changes.

Default Label Renderer

The default crosshair label is customisable using the crosshair label renderer option as shown below:

crosshair: {
    label: {
        renderer: labelRenderer, // Add label renderer callback function to customise label styles and content
    },
},
  • The renderer is a callback function which receives the axis value and its fractionDigits used for formatting the value at the crosshair position.
  • It returns an object with the text value as well as style attributes including color, backgroundColor and opacity for the crosshair label:
const labelRenderer = ({ value, fractionDigits }) => {
    return {
        text: value.toFixed(fractionDigits),
        color: 'aliceBlue',
        backgroundColor: 'darkBlue',
        opacity: 0.8,
    };
};

The default label HTML element uses CSS class name ag-crosshair-label. Custom CSS styling can be applied by providing a class name via the crosshair.label.className config. This class name will be added to the class list of the label's element.

For example, to set the label element's border-radius to 15px, add a custom class name to the crosshair label options:

crosshair: {
    label: {
        className: 'custom-crosshair-label',
    },
},

Then modify the style definitions in a stylesheet file:

.custom-crosshair-label {
    border-radius: 15px;
}

This is shown in the example below. Note that:

  • The default label template is used and the style definitions are overriden in the styles.css file.

Custom Label Renderer

A completely custom label can be provided by using the renderer function to return a string representing HTML content:

const labelRenderer = ({ value, fractionDigits }) => {
    return `<div class="custom-crosshair-label custom-crosshair-label-arrow">
            ${value.toFixed(fractionDigits)}</div>`;
};

The renderer function receives a single object with the axis value and fractionDigits.

The effect of applying the renderer from the snippet above can be seen in the example below.

Note that:

  • The structure of the returned DOM is up to you.
  • The elements have custom CSS class attributes, but the default class names can also be used so that the label gets the default styling.
  • The styles for the elements are defined in the external styles.css file.

API Reference