src/component/tree.js
function checkboxValues(selection) {
  return selection.select('.body')
     .selectAll('input:checked').data().map(d => d.id);
}
function checkboxValues(selection) {
  return selection.select('.body')
     .selectAll('input:checked').data().map(d => d.id);
}
function checkboxValues ( selection ) { return selection . select ( '.body' ) . selectAll ( 'input:checked' ) . data ( ) . map ( d => d . id ) ; }
Return an array of ids that are checked
@param {d3.selection} selection - selection of node content
Return an array of ids that are checked