docs: function all(firebaseRef) {
      return function(cb) {
          firebaseRef.once('value').then(function success(records) {
              var results = records.val();
  
              if (!results) {
                  return cb(null, []);
              }
  
              var list = Object.keys(results).map(function(key) {
                  return results[key];
              });
  
              cb(null, list);
          }, cb);
      };
  }