[Mohitmhatre32]

Brief Information

This pull request is:

• Bug Fix
• New Feature
• Other

What does this PR do?

Adds support for passing the associated series name as the second argument to the legend.formatter callback.

Related Issue: #21730 — Support legend.formatter(name, seriesName)

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Details

Before: What was the problem?

Previously, the legend.formatter callback received only the legend item name:

formatter(name)

This made it difficult to identify the associated series, particularly when working with data-item legends such as pie charts.

After: How does it work now?

The callback now receives both the legend item name and its associated series name:

formatter(name, seriesName)

Usage Example:

legend: {
    formatter(name, seriesName) {
        return `${seriesName}: ${name}`;
    }
}

The second argument is optional, ensuring backward compatibility with existing formatter callbacks.

• Existing callbacks that accept only name continue to work.
• String-based formatters remain unchanged.
• The associated series name is now available when needed.

Tests Added

Unit tests have been added to cover:

• Standard series legends.
• Pie chart / data-item legends.

Test File: test/ut/spec/component/legend/formatter.test.ts

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Validation & Testing

The following checks have been completed successfully:

• Focused legend formatter tests passed.
• Full unit test suite passed (196 tests).
• Type checking passed.
• ESLint passed.

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Documentation

• This PR does not require documentation changes.
• Documentation should be updated in a follow-up PR.
• Documentation changes have been submitted in apache/echarts-doc#xxx.

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Miscellaneous

Security Checking

• This PR uses security-sensitive Web APIs.

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Merging Options

• Please squash all commits into a single commit when merging.

Commit Message

feat(legend): support series name in formatter. close #21730

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Summary: This enhancement extends the legend.formatter callback with an optional seriesName argument, making it easier to associate legend items with their respective series while maintaining backward compatibility.

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