Difference of function(javascript) vs scope.function(angular function) defined in controller

Question

I want to know the difference between declaration of this two function in angular controller

function demo() {                           
};               

scope.demo = function() {                    
};

Whether this two function are similar in performance or not?,Which one is the better option?

I know only one difference that watch can be applied to a function which is in the scope means angular directive or element can't call javascript function.

Answer 1

Consider the following controller:

app.controller('Home', function($scope){
    function thisIsAPrivateMethod(){
      alert('Hello world');
    }

    $scope.thisIsAPublicScopedMethod(){
       alert("I'm shown!");
    }

    thisIsAPrivateMethod(); // will trigger the alert everytime HomeController is instansiated
});

in the view:

<div ng-controller="Home">
    <button ng-click="thisIsAPrivateMethod()">I will not work</button>
<button ng-click="thisIsAPublicScopedMethod()">I should display an alert</button>
</div>

As you see, the private method is only accessible within the controller code itself.