code: function() {
      if ("production" !== "development") {
        var owner = ReactCurrentOwner.current;
        if (owner !== null) {
          ("production" !== "development" ? warning(
            owner._warnedAboutRefsInRender,
            '%s is accessing isMounted inside its render() function. ' +
            'render() should be a pure function of props and state. It should ' +
            'never access something that requires stale data from the previous ' +
            'render, such as refs. Move this logic to componentDidMount and ' +
            'componentDidUpdate instead.',
            owner.getName() || 'A component'
          ) : null);
          owner._warnedAboutRefsInRender = true;
        }
      }
      var internalInstance = ReactInstanceMap.get(this);
      return (
        internalInstance &&
        internalInstance !== ReactLifeCycle.currentlyMountingInstance
      );
    }
docs: Checks whether or not this composite component is mounted.
  @return {boolean} True if mounted, false otherwise.
  @protected
  @final