How to use the react-mosaic-component.getLeaves function in react-mosaic-component

function changePanelLayout(state: PanelsState, layout: any): PanelsState {
  // filter saved props in case a panel was removed from the layout
  // we don't want it saved props hanging around forever
  const savedProps = pick(state.savedProps, getLeaves(layout));
  return { ...state, savedProps, layout };
}

determineWorkspaceLayout() {
    const { windows, layout } = this.props;
    const sortedWindows = toPairs(windows)
      .sort((a, b) => a.layoutOrder - b.layoutOrder).map(val => val[0]);
    const leaveKeys = getLeaves(layout);
    // Windows were added
    if (!sortedWindows.every(e => leaveKeys.includes(e))) {
      // No current layout, so just generate a new one
      if (leaveKeys.length < 2) {
        return createBalancedTreeFromLeaves(sortedWindows);
      }
      // Add new windows to layout
      const addedWindows = difference(sortedWindows, leaveKeys);
      const newLayout = new MosaicLayout(layout);
      newLayout.addWindows(addedWindows);
      return newLayout.layout;
    }
    // Windows were removed (perhaps in a different Workspace). We don't have a
    // way to reconfigure.. so we have to random generate
    if (!leaveKeys.every(e => sortedWindows.includes(e))) {
      return createBalancedTreeFromLeaves(sortedWindows);