Hooks

WIP

This page is a work in progress.

Hooks are named extension points registered on a chart instance with addHook(). There is currently one hook type.

TooltipHookState and TooltipHookItem, named below for clarity, are not exported by the package. TypeScript still checks the callback correctly when you call addHook("tooltip:items", callback). You just can’t import these names to write the callback’s type separately.

tooltip:items

Type: (state: TooltipHookState) => TooltipHookItem[]

Called every time the tooltip is shown, for every chart type. Return additional tooltip items to append to the tooltip. See the tooltip guide for a worked example.

Argument: TooltipHookState

Property	Type	Notes
xAxisValue	number | string | null	Set in line charts. null in bar charts.
yAxisValue	number | string | null	Set in bar charts, for the value shown on the category axis. null in line charts.
groupValue	string | null	Currently always null. No chart type sets it.
data	DataList	The data points currently shown in the tooltip, not the full data array.

Return: TooltipHookItem[]

An array of:

Property	Type	Notes
key	string	The item’s label.
value	string | number	The item’s value. A number is formatted with the axis’s extended formatter; NaN is replaced with tooltip.undefinedLabel.

Error handling

If a hook function throws, the error is logged to the console (Hook "tooltip:items" failed) and that hook’s result is skipped. Other registered hooks still run.