The error you're seeing happens because TypeScript doesn't know about the custom seriesDataItem property you've added to the legend's data context—by default, dataContext is typed as a generic Object, which doesn't include that property. Here's how to fix this with proper TypeScript typing:

Step 1: Define a Custom Interface for Legend Data #

First, create an interface that describes the structure of the data you're passing to the legend. This tells TypeScript exactly what properties to expect:

import type { SeriesDataItem, Color } from "@amcharts/amcharts4";

interface LegendEntry {
  name: string;
  fill: Color;
  seriesDataItem: SeriesDataItem;
}

(Note: If you haven't already, install AmCharts 4 type definitions with npm install @types/amcharts4 --save-dev)

Step 2: Update the Event Handler with Typed Data #

Rewrite your code to use this interface, ensuring TypeScript recognizes the seriesDataItem property in the data context:

series2.events.on("dataitemsvalidated", () => {
  const legendData: LegendEntry[] = [];

  series2.dataItems.each((dataItem) => {
    legendData.push({
      name: `${dataItem.categoryY}: ${dataItem.valueX}%`,
      fill: dataItem.column.fill!, // Non-null assertion: use only if you're sure fill exists
      seriesDataItem: dataItem
    });
  });

  chart.legend.data = legendData;

  chart.legend.itemContainers.template.events.on("toggled", (event) => {
    // Cast the dataContext to our custom interface
    const legendEntry = event.target.dataItem.dataContext as LegendEntry;
    const seriesDataItem = legendEntry.seriesDataItem;

    console.log(seriesDataItem);

    if (event.target.isActive) {
      seriesDataItem.hide(series2.interpolationDuration, 0, 0, ["valueX"]);
    } else {
      seriesDataItem.show(series2.interpolationDuration, 0, ["valueX"]);
    }
  });
});

Key Fixes Explained: #

• Typed Legend Data: By declaring legendData as LegendEntry[], TypeScript knows every item in the array has a seriesDataItem property.
• Casting Data Context: Using as LegendEntry tells TypeScript that the dataContext conforms to our custom interface, eliminating the type error when accessing seriesDataItem.
• Non-Null Assertion: The ! after dataItem.column.fill assumes that fill is always present. If there's a chance it could be null, replace it with optional chaining (dataItem.column?.fill) and handle the undefined case.

This approach keeps your code type-safe while maintaining the original functionality of toggling series items via the legend.

内容的提问来源于stack exchange，提问作者Praveen