Access local variable of another function in AngularJS

declare modalInstance outside of the functions. This will scope it to the whole controller.

myApp.controller "RegistrationsController", ($scope, $location, $http, $modal)->

  var modalInstance;

  $scope.open = () ->
    # move to global
    modalInstance = $modal.open(
      templateUrl: "/assets/angular/templates/registrations/_signup.html",
      controller: "ModalController"
    )
  $scope.cancel = ->
    modalInstance.dismiss('cancel')
  $scope.saveUser = () ->
    $scope.cancel()

If you're trying to cancel from the ModalController then you can add inject the $modalInstance dependency like ...

.controller('ModalController', function($scope, $modalInstance) {
   $scope.cancel = function() {
     $modalInstance.dismiss('cancel');
   };
});

If you're trying to cancel it from anywhere else then you can share you're controller among other directives using require? Like

.directive('otherDirective', function() {
   return {
     require: 'RegistrationController',
     link: function(scope, el, attr, ctrl) {

     }
   }
});

Or you could use a service as mediator between other controllers, services, directive, what ever.

.service('mediator', function() {
   var modalInstance;

   this.modalInstance = function(instance) {
     if (instance) {
       modalInstance = instance;
     }

     return modalInstance;
   };
});

and then in your directives and controllers and what not, do something like...

.controller('SomeController', function(mediator) {

   this.cancel = function() {
     mediator.modalInstance().dismiss('cancel');
   });
});

You can amend for CoffeeScript ;)