Its index into the series' data list, which is how it is named.
Optionalid
id?:string
What the links name it by: the data item's id, or its name when it
declared none. Measured unique within the series -- ECharts refuses a
second node with the same id.
One node of a graph series.
There is no
name: reading one givesundefined. A node is named throughEChartsList.getName(node.dataIndex), or equivalently by itsid.