javascript - How to use promises correctly with callback function -

i've service, returns list of students asynchronously using callback:

    studentmodule.factory('studentservice', function (db_url) {         return {             getallstudents: function (callback) {                 var datastore = require('nedb'),                     path = require('path');                 db = {};                 db.students = new datastore({                     filename: db_url + '/students.db',                     autoload: true                 });                 db.students.find({}, function (err, stds) {                     callback(stds);                 });             }; //end return  

my old way use in controller:

studentservice.getallstudents(function(sts) {     $scope.students = sts;     $scope.$apply();//notify angular change }); 

this works me, want use best practices. need resolve result in route before coming controller, here did:

.state('payment', {     url: '/payment',     templateurl: 'frontend/components/payment/views/payment.html',     controller: 'paymentcontroller',     resolve: {         students: function (studentservice, $q) {             var defer = $q.defer();             defer.promise.then(function () {                 studentservice.getallstudents(function (sts) {                     alert(json.stringify(sts));                     return sts;                 });             })             defer.resolve();         }     } }) 

the alert returning data route not controller - undefined in controller:

paymentmodule.controller('paymentcontroller', function($scope,students) {     alert(json.stringify(students)); 

any appreciated!

you should return promise resolve functions, and, when creating promise of own, should resolve data need pass along it.

.state('payment', {     url: '/payment',     templateurl: 'frontend/components/payment/views/payment.html',     controller: 'paymentcontroller',     resolve: {         students: function (studentservice, $q) {             var defer = $q.defer();             //defer.promise.then(function () {             studentservice.getallstudents(function (sts) {                 //alert(json.stringify(sts));                 //return sts;                 defer.resolve(sts);             });             //})             //defer.resolve();             return defer.promise         }     } })