listener.jsx

class Component extends React.Component {
  constructor(props) {
    super(props);
    this.initialState = {
      isBelowScrollLine: false
    };
    this.scrollListener = this.scrollListener.bind(this);
  }
  componentDidMount() {
    window.requestAnimationFrame(this.scrollListener);
  }
  scrollListener() {
    const isBelowScrollLine = // logic to determine if we are passed the point you want.
    
    if (isBelowScrollLine && !this.state.isBelowScrollLine) {
      this.setState({ isBelowScrollLine: true });
    } else if (!isBelowScrollLine && this.state.isBelowScrollLine) {
      component.setState({ isBelowScrollLine: false });
    }
    
    window.requestAnimationFrame(this.scrollListener);
  }
  render() {
    // some pretty crap
  }
}