index.js

render() {
    const { isLoading, token } = this.state;

    if (!isLoading) {
      if (!token) {
        return (
          <Login screenProps={{ logIn: this.logIn }} />
        );
      } else {
        return (
          <Root
            screenProps={{
              logOut: this.logOut,
            }}
          />
        );
      }
    } else {
      return null;
    }
  }