How to use the react-static.onLoading function in react-static

componentDidMount () {
    onLoading(loading => {
      if (loading) {
        nprogress.start()
      } else {
        nprogress.done()
      }
    })
  }
  render () {

componentDidMount () {
    onLoading(loading => {
      if (loading) {
        NProgress.start()
      } else {
        NProgress.done()
      }
    })

    if (window) {
      window.addEventListener('resize', this.updateDimensions)
      this.setState({
        width: window.innerWidth,
        sidebarIsOpen: window.innerWidth > 700,
      })
    }
  }

componentDidMount() {
    onLoading(loading => {
      if (loading) {
        nprogress.start();
      } else {
        nprogress.done();
      }
    });
  }
  render() {

componentDidMount() {
        onLoading(loading => {
            if (loading) {
                nprogress.start();
            } else {
                nprogress.done();
            }
        });
    }