backbone-router-filter.js

(function(Backbone, _) {
	var leave, leaveArgs;

	_.extend(Backbone.Router.prototype, Backbone.Events, {
		route : function(route, name, callback) {
			if(!callback)
				callback = this[name];

			var before
				, fn = callback
				, after;

			Backbone.history || (Backbone.history = new Backbone.History);

			if(!_.isRegExp(route))
				route = this._routeToRegExp(route);

			if(!fn)
				fn = this[name];

			if(typeof callback == 'object'){
				before = callback.before;
				fn = callback.route;
				after = callback.after;
			}

			Backbone.history.route(route, _.bind(function(fragment) {
				var args = this._extractParameters(route, fragment);

				if(leave) {
					if(leave.apply(this, leaveArgs) === false)
						return;
					else
						leave = false;
				}

				if(before && before.apply(this, args) === false) return;

				fn.apply(this, args);

				if(after && after.apply(this, args) === false) return;

				if(typeof callback == 'object') {
					leave = callback.leave;
					leaveArgs = args;
				}

				this.trigger.apply(this, ['route:' + name].concat(args));

				Backbone.history.trigger('route', this, name, args);
			}, this));
			
			return this;
		}
	});
}).call(this, Backbone, _);

routes-example.js

{
  routes: {
    'index': 'index'
  },

  index: {
    before: function(){},
    route: function(){}, // Main route function
    after: function(){},
    leave: function(){}
  }
}