How to access controller functions in directive link?

Question

How to access directive controller functions from directive link? Bellow controller passed to link is empty, I would like to get in it show() hide() functions.

My current directive:

app.directive('showLoading', function() {
  return {
    restrict: 'A',
    // require: 'ngModel',
    scope: {
      loading: '=showLoading'
    },
    controller: function($scope, $element) {
      return {
        show: function() {
          alert("show");
        },
        hide: function() {
          alert("hide");
        }
      };
    },
    link: function($scope, $element, $attrs, controller) {
      $scope.$watch('loading', function(bool) {
        if (bool) {
          controller.show();//undefined
        } else {
          controller.hide();
        }
      });
    }
  };
});

Solution

Publishing on the scope can work, but not the best practice, since it "pollutes" the scope. The proper way to communicate with own controller is to require it - then it will become available as a parameter to the link function, along with other required directives.

The other issue is with how you expose functions on the controller - this is done by using this.someFn, not by returning an object.

app.directive('showLoading', function() {
  return {
    restrict: 'A',
    require: ['ngModel', 'showLoading'], // multiple "requires" for illustration
    scope: {
      loading: '=showLoading'
    },
    controller: function($scope, $element) {
      this.show = function() {
        alert("show");
      };

      this.hide = function() {
        alert("hide");
      };
    },
    link: function($scope, $element, $attrs, ctrls) {
      var ngModel = ctrls[0], me = ctrls[1];

      $scope.$watch('loading', function(bool) {
        if (bool) {
          me.show();
        } else {
          me.hide();
        }
      });
    }
  };
});