code: function findAll(collection, callbacks) {
    localforage.getItem(collection.sync.localforageKey, function(err, data) {
      if (data && data.length) {
        var done = function() {
          if (callbacks.success) {
            callbacks.success(data.filter(function (model) {
              // Because the collection is stored as a list of model keys, some
              // keys may point to models that no longer exist. localForage
              // returns those as null, so just filter those out for now, and
              // when a new model is saved, the list of keys will be updated to
              // match existing models.
              return model !== null;
            }));
          }
        };
  
        // Only execute `done` after getting all of the
        // collection's models.
        done = after(data.length, done);
  
        var onModel = function(i, err, model) {
          data[i] = model;
          done();
        };
  
        for (var i = 0; i < data.length; ++i) {
          localforage.getItem(data[i], partial(onModel, i));
        }
      } else {
        data = [];
        if (callbacks.success) {
          callbacks.success(data);
        }
      }
    });
  }
docs: Only used by `Collection#sync`.