Router: transitionToPrevious and intermediateTransitionToPrevious

router.js

var AppRouter = Router.extend({
  previousHandlers: null,
  currentHandlers: null,

  transitionChanged: function() {
    var previousHandlers = this.router.oldState.handlerInfos;
    this.set('previousHandlers', previousHandlers);

    var currentHandlers = this.router.currentHandlerInfos;
    this.set('currentHandlers', currentHandlers);
  }.on('didTransition'),

  intermediateTransitionToPrevious: function() {

    var handlers = this.get('currentHandlers');
    if (!handlers || !handlers.length) { return; }

    var handler = handlers[handlers.length - 1];

    var args = _getModels(handlers);
    args.unshift(handler.name);
    //handlerName, model1, model2....
    return this.intermediateTransitionTo.apply(this, args);

  },

  transitionToPrevious: function(errorCallback) {

    var handlers = this.get('previousHandlers');
    if (!handlers || !handlers.length) { return; }

    var handler = handlers[handlers.length - 1];
    if (handler.name === 'loading') {
      if (errorCallback) { return errorCallback(); }
      return;
    }
    var args = _getModels(handlers);
    args.unshift(handler.name);
    //handlerName, model1, model2....
    return this.transitionTo.apply(this, args);

  }

});

AppRouter.map(Routes);

var _getModels = function(handlers) {

  var result = [],
      length,
      context,
      params,
      handler;

  for (var i = 0; i < handlers.length; i++) {
    handler = handlers[i];
    params = handler.params;
    length = Object.keys(params).length;
    context = handler.context;

    if (length && context) {
      //is isNew and 1 parameter, this could be the
      //route `new` pattern
      if (context.get('isNew') && length === 1) {
        result.push(params[Object.keys(params)[0]]);
      } else {
        result.push(handler.context);
      }
    }
  }
  return result;
};