angularjs - Angular $http difference between .success() and .then() -

sometimes have trouble fetch data using $http service. , did not 100% understand main difference between .success() , .then()

the following example can fetch data using $http().then(), can't fetch data using $http().success(). can explain why?

code using $http.success() http://jsfiddle.net/xoonplte/11/

var manurep = angular.module('manurep', ['ui.bootstrap']);   manurep.controller('myappcontroller', function($scope, $http) {     $http.get('https://dl.dropboxusercontent.com/u/59954187/jobs.json').       success(function(response) {         $scope.cats = response.data;           }).       error(function(error){         alert(json.stringify(error));       return error;       });   }); 

code using $http.then() http://jsfiddle.net/xoonplte/12/

var manurep = angular.module('manurep', ['ui.bootstrap']);   manurep.controller('myappcontroller', function($scope, $http) {     $http.get('https://dl.dropboxusercontent.com/u/59954187/jobs.json').       then(function(response) {         $scope.cats = response.data;           });   }); 

.then promises

.success , .error callback.

why callbacks or promises?

1 . promises can handle global errors.
2 . promises can chained (you don't have encapsulation callbacks)

p = promise,
r = response,
e = error.

1:

p1(r1) .p2(r2) .p3(r3, e3)   

error 3 called if there error in promise 1, 2 or 3.
not possible callbacks.

2:
if have 3 promises:

p1(r1, e1) .p2(r2, e2) .p3(r3,e3) 

if have 3 callbacks

p1().success(p2().success(p3().success().error()).error()).error() 

edit

.service('auth', function(){   this.isloggedin = function(){      return $http.get('url/isloggedin');   }; })  .service('getdata', function(){   this.name = function(){     return $http.get('url/data/name');   } })  .controller('myctrl', ['auth', 'getdata', function(auth, getdata){     auth.isloggedin().then(function(resp){      return getdata.name(); //by sending value inthe response, next response called    })    .then(function(res){         //here     }, function(err){         //global error.         //this called in p1 or p2     })   }]);