src/event-emitter.js
function internal(obj) {
  if (!privateMap.has(obj)) {
    privateMap.set(obj, {});
  }

  return privateMap.get(obj);
}
function internal(obj) {
  if (!privateMap.has(obj)) {
    privateMap.set(obj, {});
  }

  return privateMap.get(obj);
}
function internal ( obj ) { if ( ! privateMap . has ( obj ) ) { privateMap . set ( obj , { } ) ; } return privateMap . get ( obj ) ; }
For making private properties.
For making private properties .