gistfile1.js

var Filter = Backbone.Model.extend({
  initialize: function(options){

    if( options.globalFilter ){
      this.globalFilter = options.globalFilter;
      this.set( this.globalFilter.toJSON() );
      this.listenTo( this.globalFilter, 'change', function(){
        this.set( this.globalFilter.toJSON() );
      }, this );
    }

  }
});