code: function fitExtent(state, action) {
    const extent = action.extent;
    const resolution = getResolutionForExtent(extent, action.size, action.projection);
    const zoom = getZoomForResolution(resolution, action.projection);
    const center = [(extent[0] + extent[2]) / 2, (extent[1] + extent[3]) / 2];
    return Object.assign({}, state, {center, zoom});
  }
docs: Fit the extent on the map. Can be used to zoom to a layer for instance.
  @param {Object} state Current state.
  @param {Object} action Action to handle.
  
  @returns {Object} The new state.