code: function storagePushToSet([key, value]) {
      log('storagePushToSet', key, value);
  
      const item = getLocalStorageItem(key);
      const list = Array.isArray(item) ? item : [];
  
      if (list.indexOf(value) === -1) {
        list.push(value);
      }
  
      setLocalStorageItem(key, list);
    }
docs: A Set is a list with only unique values. (No duplication.)