FooPage.jsx

class FooPage {
  
  async loadData () {
    const data = await getData()
    this.setState({ data })
  }
  
  render () {
    return (
      <Page data={this.state.data} loadData={this.loadData}>
        {data => (
          <div>{data.foo.bar}</div>
        )}
      </Page>
    )
  }
}

Page.jsx

class Page {
  
  constructor () {
    this.state = { loading: true }
  }
  
  componentDidMount () {
    await this.props.loadData()
    this.setState({ loading: false })
  }
  
  render () {
    if (this.state.loading)
      return <div>Loading!</div>
    else
      return this.props.children(data)
  }
  
}