lib/j2119/role_finder.js
function descendantRoles (roles, fieldName, allDescendants) {
  return roles
    .map(role => allDescendants.get(role))
    .filter(descendants => !!descendants)
    .map(descendants => descendants.get(fieldName))
    .filter(fieldRoles => !!fieldRoles)
}
function descendantRoles (roles, fieldName, allDescendants) {
  return roles
    .map(role => allDescendants.get(role))
    .filter(descendants => !!descendants)
    .map(descendants => descendants.get(fieldName))
    .filter(fieldRoles => !!fieldRoles)
}
class RoleFinder