1. @Deprecated("Internal Use Only")
void finalizeJsInterfaces()

Can be called to provide a predictable point where no more JS interfaces can be added. Creating an instance of JsObject will also automatically trigger all JsObjects to be finalized.

Source 

@Deprecated("Internal Use Only")
void finalizeJsInterfaces() {
  if (_finalized == true) {
    throw 'JSInterop class registration already finalized';
  }
  _finalizeJsInterfaces();
}