Cannot set property from angularjs service - angularjs

Question

I am trying to set value in html page from angularjs controller.
I am getting value from web api in service but I have issue that I am always getting error:
TypeError: Cannot set property 'messageFromServer' of undefined
But I can't figure what am I doing wrong here. What am I missing?
On the html part I have:
<div ng-app="myApp" ng-controller="AngularController">
<p>{{messageFromServer}}</p>
</div>
In the controller I have:
var app = angular.module('myApp', []);
app.controller('AngularController', ['$scope', 'messageService', function ($scope, messageService) {
$scope.messageFromServer = "When I set it here it works!"
messageService.getMessage();
}]);
app.service('messageService', ['$http', function ($http) {
this.getMessage = function ($scope) {
return $http({
method: "GET",
url: "api/GetMessage",
headers: { 'Content-Type': 'application/json' }
}).success(function (data) {
$scope.messageFromServer = data;
console.log(data);
}).error(function (data) {
console.log(data);
})
};
}]);

Answer 1

Basically the problem is, you missed to $scope object to the service getMessage method. But this is not a good approach to go with. As service is singleton object, it shouldn't manipulate scope directly by passing $scope to it. Rather than make it as generic as possible and do return data from there.
Instead return promise/data from a service and then assign data to the scope from the controller .then function.
app.service('messageService', ['$http', function ($http) {
this.getMessage = function () {
return $http({
method: "GET",
url: "api/GetMessage",
headers: { 'Content-Type': 'application/json' }
}).then(function (response) {
//you could have do some data validation here
//on the basis of that data could be returned to the consumer method
//consumer method will have access only to the data of the request
//other information about request is hidden to consumer method like headers, status, etc.
console.log(response.data);
return response.data;
}, function (error) {
return error;
})
};
}]);
Controller
app.controller('AngularController', ['$scope', 'messageService',
function ($scope, messageService) {
$scope.messageFromServer = "When I set it here it works!"
messageService.getMessage().then(function(data){
$scope.messageFromServer = data;
});
}
]);

Answer 2

Don't use $scope in your service, just return the promise from $http.
var app = angular.module('myApp', []);
app.service('messageService', ['$http', function ($http) {
this.getMessage = function () {
return $http({
method: "GET",
url: "api/GetMessage",
headers: { 'Content-Type': 'application/json' }
});
};
}]);
app.controller('AngularController', ['$scope', 'messageService', function ($scope, messageService) {
messageService.getMessage().then(function(data) {
$scope.messageFromServer = data;
});
}]);
In this example you can unwrap the promise in your controller, or even better you can use the router to resolve the promise and have it injected into your controller.
app.config(function($routeProvider) {
$routeProvider.when('/',{
controller: 'AngularController',
templateUrl: 'views/view.html',
resolve: {
message: function(messageService) {
return messageService.getMessage();
}
}
});
});
Then in your AngularController, you'll have an unwrapped promise:
app.controller('AngularController', ['$scope', 'message', function ($scope, message) {
$scope.messageFromServer = message;
}]);