feat(tooltip): add series name as third parameter to valueFormatter (#21459)

[Mustansir-06]

This PR adds the series name as a third argument to the valueFormatter function in the tooltip component.

Currently, valueFormatter only receives value and dataIndex. Adding the name (series name) allows users to perform conditional formatting based on the series without having to write a full custom formatter HTML string.

Changes
src/component/tooltip/tooltipMarkup.ts: Updated buildNameValue to pass fragment.name into the valueFormatter call.

src/util/types.ts: Updated the CommonTooltipOption and TooltipValueFormatter types to include the optional name?: string parameter to ensure TypeScript compatibility.

[echarts-bot]

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[plainheart]

valueFormatter is designed for the tooltip of a single series rather than the global tooltip option. See this demo for recommended usage.

[Mustansir-06]

Thank you for the demo and the feedback @plainheart!

I agree that defining individual formatters works well for a few series. However, the motivation for this PR is to support generic, reusable formatting functions.

If a developer has many series (or a dynamic number of series), they currently have to define a new function for each one to include the series name. By passing the name as a third parameter, a single formatter can be written to handle multiple series dynamically:
// With this PR, one function can handle multiple units dynamically
const myGenericFormatter = (value, index, name) => {
const unitMap = { 'Email': ' unit1', 'Union Ads': ' unit2' };
return value + (unitMap[name] || '');
};
This brings valueFormatter in line with other ECharts formatters that already provide the name context. What are your thoughts on supporting this more dynamic approach?

[plainheart]

Thanks for your suggestions and work! I don't think it's worth adding a new callback parameter when there's a feasible and less cumbersome solution available, so I'd rather not add it — unless we receive more requests for this feature from developers.

[plainheart]

If a developer has many series (or a dynamic number of series), they currently have to define a new function for each one to include the series name

This can be done with a loop. Demo

[Mustansir-06]

Thank you for the demo, @plainheart!

I see how using a closure within the series.forEach loop effectively captures the series context without needing an additional parameter in the valueFormatter callback. It's a clean way to handle the requirement using the existing API.

I appreciate the time you took to review this and for providing the alternative approach. I'll close this PR for now. Thanks again!