Type export missing for tooltip formatter callback

[Bilge]

What problem does this feature solve?

It is difficult to write a tooltip formatter in a typed application because it seems the necessary type is not exported. As far as I can tell, the type is declared as TooltipFormatterCallback<TopLevelFormatterParams>, but since the type is not exported in 5.0.2, it cannot be consumed in the user's application.

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[plainheart]

Related to #14277. It seems this type should be exported indeed.

Currently, as a workaround, we can get it like this, (slightly complicated)

import { TooltipComponentOption } from 'echarts/components'

type Unified<T> = Exclude<T, T[]>
type TooltipFormatterCallback = Exclude<NonNullable<TooltipComponentOption['formatter']>, string>
// single and multiple params
type TooltipFormatterParams = Parameters<TooltipFormatterCallback>[0]
// single params
type SingleTooltipFormatterParams = Unified<TooltipFormatterParams>
// multiple params
type MultipleTooltipFormatterParams = SingleTooltipFormatterParams[]

const formatter0: TooltipFormatterCallback = (params: TooltipFormatterParams) => {
  if (Array.isArray(params)) {
    return params[0].seriesName || ''
  }
  return params.seriesName || ''
}

const formatter1: TooltipFormatterCallback = (params: SingleTooltipFormatterParams) => {
  return params.seriesName || ''
}

const formatter2: TooltipFormatterCallback = (params: MultipleTooltipFormatterParams) => {
  return params[0].seriesName || ''
}

[Ovilia]

Please follow #14277 for future information.