Edit in JSFiddle

var app = angular.module('myApp', []);

//---------------------------------------------------------------------------------
app.service('myService', ['$http', '$rootScope', function ($http, $rootScope) {
    // data private access
    var inData = {
        cpt: 0,
        mytext: 'hello who ?',
        extData: undefined
    };

    var loadData = function () {
        console.log("loadData");
        var data = {
            "hello": 'world'
        };
        return $http.post('/echo/json/', 'json=' +  encodeURIComponent(angular.toJson(data)), {
            headers: {
                'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
            }
        });
    };

    // data public access with getter setter
    this.outData = {
        get extData() {
            console.log("get extData");
            if (!inData.extData) {
                inData.extData = "loading ..."; // init to avoid loop loading
                var myPromise = loadData();
                myPromise.then(function (response) {
                    console.log("myPromise success");
                    inData.extData = response.data;
                    $rootScope.$$phase || $rootScope.$apply();
                }, function (response) {
                    console.log("myPromise error");
                    inData.extData = "error";
                    $rootScope.$$phase || $rootScope.$apply();
                });
            }
            return inData.extData;
        },
        get cpt() {
            console.log("get cpt");
            return inData.cpt;
        },
        get text() {
            console.log("get text");
            return inData.mytext;
        },
        set text(val) {
            console.log("set text");
            inData.cpt = inData.cpt + 1;
            inData.mytext = val;
        }
    };

    this.showData = function () {
        console.log('nb update ' + inData.cpt);
    };

}]);

//---------------------------------------------------------------------------------
app.controller('MainCtrl', ['$scope', 'myService', function ($scope, myService) {
    console.log('online');
    $scope.data = myService.outData;
        
    $scope.showData = function () {
        myService.showData();
    };
}]);

<div data-ng-controller="MainCtrl">
     <h1>text: {{data.text}}</h1>
    <input type="text" data-ng-model="data.text" />
     <h2>nb update: {{data.cpt}}</h2>
    <button type="button" data-ng-click="showData()">Show</button>
     <h2>text: {{data.extData}}</h2>
</div>