render props exposes API

exporesAPI.js

class Hello extends React.Component {
  state = { isSubmitting: false }
  
  handleThisClick = () => {
    /* do your thing here */
  }
  
  handleFormSubmit = async event => {
    event.preventDefault();
    
    this.setState({ isSubmitting: true })
    
    try {
      const response = await fetch(/* stuffs */)
      this.setState({ isSubmitting: false })
    } catch(err) {
      console.log(err);
    }
  }

  render() {
    return (
      {this.props.children({
          handleFormSubmit: this.handleFormSubmit, 
          handleThisClick: this.handleThisClick,
          isSubmitting: this.state.isSubmitting
      })}  
    )
  }
}