medium-test-directive-user-display.controller.js

.controller('userDisplayController', function(followService) {
  var self = this;

  self.toggleFollow = toggleFollow;
  self.isFollowing = followService.isFollowing(self.user);

  function toggleFollow() {
    if (isFollowing) {
      followService.unfollow(self.user);
      self.isFollowing = false;
    } else {
      followService.follow(self.user);
      self.isFollowing = true;
    }
  }
})