How to configure the style of the legend separately in VChart and change the shape of the graphic

Question title

How to configure the style of legends separately in VChart and change the shape of graphics

Problem description

How to change the legend item graphic of a column chart series to a circle

Solution

Legends in VChart can be customized through the data configuration item, where the graphic property is in the shapeproperty of the legend item

 legends: {
    visible: true,
    data: items => {
      return items.map(item => {
        if(item.label === 'Under 5 Years'){
          item.shape.symbolType = 'circle';
        }
        return item;
      });
    },
  },

Code example

const spec = {
  type: 'bar',
  data: [
    {
      id: 'barData',
      values: [
        {
          State: 'WY',
          Age: 'Under 5 Years',
          Population: 25635
        },
        {
          State: 'WY',
          Age: '5 to 13 Years',
          Population: 1890
        },
        {
          State: 'WY',
          Age: '14 to 17 Years',
          Population: 9314
        },
        {
          State: 'DC',
          Age: 'Under 5 Years',
          Population: 30352
        },
        {
          State: 'DC',
          Age: '5 to 13 Years',
          Population: 20439
        },
        {
          State: 'DC',
          Age: '14 to 17 Years',
          Population: 10225
        },
        {
          State: 'VT',
          Age: 'Under 5 Years',
          Population: 38253
        },
        {
          State: 'VT',
          Age: '5 to 13 Years',
          Population: 42538
        },
        {
          State: 'VT',
          Age: '14 to 17 Years',
          Population: 15757
        },
        {
          State: 'ND',
          Age: 'Under 5 Years',
          Population: 51896
        },
        {
          State: 'ND',
          Age: '5 to 13 Years',
          Population: 67358
        },
        {
          State: 'ND',
          Age: '14 to 17 Years',
          Population: 18794
        },
        {
          State: 'AK',
          Age: 'Under 5 Years',
          Population: 72083
        },
        {
          State: 'AK',
          Age: '5 to 13 Years',
          Population: 85640
        },
        {
          State: 'AK',
          Age: '14 to 17 Years',
          Population: 22153
        }
      ]
    }
  ],
  xField: 'State',
  yField: 'Population',
  seriesField: 'Age',
  stack: true,
  legends: {
    visible: true,
    data: items => {
      return items.map(item => {
        if(item.label === 'Under 5 Years'){
          item.shape.symbolType = 'circle';
        }
        return item;
      });
    },
  },
  bar: {
    // The state style of bar
    state: {
      hover: {
        stroke: '#000',
        lineWidth: 1
      }
    }
  }
};

const vchart = new VChart(spec, { dom: CONTAINER_ID });
vchart.renderSync();

// Just for the convenience of console debugging, DO NOT COPY!
window['vchart'] = vchart;