live.js

  var LiveCollection = Backbone.Collection.extend({
    ...
    
    _createEvent: function(body) {
      ...
      
      // Look to see if this collection has any outstanding creates...
      var idAttribute = this.model.prototype.idAttribute;
      var unsaved = this.filter(function(model) {
        return !model.id;
      });

      // If there are unsaved items, monitor them and if one of them turns out to be the matching object
      // then simply update that
      if(unsaved.length) {
        console.log('live: awaiting syncs of unsaved objects');

        var listener = new UpdateEventListener(id, unsaved);

        listener.once('notfound', function() {
          this.add(body, { parse: true });
        }, this);

      } else {
        this.add(body, { parse: true });

      }
    }
    ...
  });
  
  
  function UpdateEventListener(outstandingId, models) {
    this._outstandingId = outstandingId;
    this._awaitCount = models.length;

    _.each(models, function(model) {
      this.listenToOnce(model, 'sync error', this._onModelSync);
    }, this);
  }

  _.extend(UpdateEventListener.prototype, Backbone.Events, {
    _onModelSync: function(model) {
      if(model.id === this._outstandingId) {
        // Great, this is the model we're waiting for!
        this.trigger('found', model);
        this.stopListening();

      } else if(--this._awaitCount === 0) {
        // All the models are done and we haven't found the id we received from the realtime stream
        this.stopListening();
        this.trigger('notfound');
      }
    }
  });