code: function getLayerGroupName(layer_group) {
    const all_names = [];
    for (let i = 0, ii = layer_group.length; i < ii; i++) {
      all_names.push(layer_group[i].id);
    }
    return `${layer_group[0].source}-${all_names.join(',')}`;
  }
docs: Create a unique key for a group of layers
  @param {Object[]} layer_group An array of Mapbox GL layers.
  
  @returns {string} The layer_group source name, followed by a concatenated string of layer ids.