code: public static boolean isEs6ModuleRoot(Node scriptNode) {
      checkArgument(scriptNode.isScript(), scriptNode);
      if (scriptNode.getBooleanProp(Node.GOOG_MODULE)) {
        return false;
      }
      return scriptNode.hasChildren() && scriptNode.getFirstChild().isModuleBody();
    }
docs: Return whether or not the given script node represents an ES6 module file.