Extracts the D3-bound datum from a DOM element. D3.js stores bound data on the __data__ property of DOM elements after a .data() join.
__data__
.data()
The DOM element to extract data from.
The bound datum, or undefined if no data is bound.
undefined
Extracts the D3-bound datum from a DOM element. D3.js stores bound data on the
__data__property of DOM elements after a.data()join.