code: function orderLayer(state, action) {
    let layer = null, target = null;
    for (let i = 0, ii = state.layers.length; i < ii; i++) {
      if (state.layers[i].id === action.layerId) {
        layer = state.layers[i];
      }
      if (state.layers[i].id === action.targetId) {
        target = state.layers[i];
      }
    }
  
    if (layer !== null) {
      let targetId = action.targetId;
      let targetGroup = getGroup(target);
      let layerGroup = getGroup(layer);
      if (layerGroup !== targetGroup) {
        targetId = changeTarget(state, action);
      }
      if (targetId !== false) {
        return placeLayer(state, layer, targetId);
      }
    }
    return state;
  }
docs: Change the order of the layer in the stack.
  @param {Object} state Current state.
  @param {Object} action Action to handle.
  
  @returns {Object} The new state.