Can't get result data with $http angularjs - http

Question

I'm trying to use $http, but why it return null result?
angular.module('myApp')
.factory('sender', function($http) {
var newData = null;
$http.get('test.html')
.success(function(data) {
newData = data;
console.log(newData)
})
.error(function() {
newData = 'error';
});
console.log(newData)
return newData
})
Console say: http://screencast.com/t/vBGkl2sThBd4. Why my newData first is null and then is defined? How to do it correctly?

Answer 1

As YardenST said, $http is asynchronous so you need to make sure that all functions or display logic that are dependent on the data that is returned by your $http.get(), gets handle accordingly. One way to accomplish this is to make use of the "promise" that $http returns:
Plunkr Demo
var myApp = angular.module('myApp', []);
myApp.factory('AvengersService', function ($http) {
var AvengersService = {
getCast: function () {
// $http returns a 'promise'
return $http.get("avengers.json").then(function (response) {
return response.data;
});
}
};
return AvengersService;
});
myApp.controller('AvengersCtrl', function($scope, $http, $log, AvengersService) {
// Assign service to scope if you'd like to be able call it from your view also
$scope.avengers = AvengersService;
// Call the async method and then do stuff with what is returned inside the function
AvengersService.getCast().then(function (asyncCastData) {
$scope.avengers.cast = asyncCastData;
});
// We can also use $watch to keep an eye out for when $scope.avengers.cast gets populated
$scope.$watch('avengers.cast', function (cast) {
// When $scope.avengers.cast has data, then run these functions
if (angular.isDefined(cast)) {
$log.info("$scope.avengers.cast has data");
}
});
});

Answer 2

This JavaScript code is asynchronous.
console.log(newData)
return newData
Is executed before what inside success
newData = data;
console.log(newData)
So at first time, the newData is null (you set it to be null)
And when the http response is returned (inside the success), the newData gets its new value.
This is very common in Javascript, you should do all your work inside the success.