$window on ngClick directive - angularjs

Question

Why this doesn't work ?
Since angular expression doesn't have access to window object, i've used $window, however the below doesn't work.
<button ng-click="$window.alert('Hi There')">Hi There</button>
Angular expressions do not have access to global variables like
window, document or location. This restriction is intentional. It
prevents accidental access to the global state – a common source of
subtle bugs.

Answer 1

A template only has access to variables that are put on its $scope. If you need to access anything on $window from your template you'll need to inject $window into your controller and assign it to $scope there.
For example
angular.module('app').controller('Controller',
['$scope', '$window', function($scope, $window) {
$scope.$window = $window;
}]);
As pointed out in the comments, you probably don't want to expose the entire $window wrapper to your template so a better approach is to use a helper function on $scope.
ng-click="greet('Hi There')"
angular.module('app').controller('Controller',
['$scope', '$window', function($scope, $window) {
$scope.greet = function(message) {
$window.alert(message);
};
}]);

Answer 2

You can only call services in your controllers through scope (this is the idea of separating non-UI logic from the template)
See How to call a service function in AngularJS ng-click (or ng-change, ...)?
$window is a service, and like other services that don't relate directly to the view, they are not accessible in the templates.
angular.module('app').controller('Controller',
['$scope', '$window', function($scope, $window) {
$scope.alert=$window.alert
}]);