constructor(...args) {
    super(...args);

    // If this component is being rendered server-side, getScrollbarSize() will return undefined.
    // We handle this case in componentDidMount()
    this._scrollbarSize = getScrollbarSize();
    if (this._scrollbarSize === undefined) {
      this._scrollbarSizeMeasured = false;
      this._scrollbarSize = 0;
    } else {
      this._scrollbarSizeMeasured = true;
    }
  }
Width of Collection; this property determines the number of visible (vs virtualized) columns.