Extending $scope

rootScope.js

angular.module("myApp").run(function ($rootScope) {
	
        var proto = Object.getPrototypeOf($rootScope);
	angular.extend(proto, {
		$waitFor: function (expression, fn) {
			var un = this.$watch(expression, function (value) {
				if (value === undefined) return;
				un();
				return fn(value);
			});
		}
	});
	
});

// example of usage in the controller
$scope.$waitFor('user', function (user) {
	$scope.userName = user.name;
});