constructor(props, context) {
    super(props, context);

    this.state = {
      clientHeight: 0,
      clientWidth: 0,
      scrollHeight: 0,
      scrollLeft: 0,
      scrollTop: 0,
      scrollWidth: 0,
    };

    this._onScroll = this._onScroll.bind(this);
  }
Function responsible for rendering 2 or more virtualized components.
This function should implement the following signature:
({ onScroll, scrollLeft, scrollTop }) => PropTypes.element