Edit in JSFiddle

<div ng-app="MyApp" ng-controller="DemoCtrl">
     <h1>{{ welcome }}</h1>

    <button ng-click="fetchUsers()">fetch some badass GitHub users data</button>
    <ul>
        <li ng-class="{odd: $odd}" ng-repeat="user in users">
            <img class="gravatar" ng-src="{{ user.profile.avatar_url }}" /> <b>{{ user.profile.login }}</b> ({{ user.profile.location }})
            <div class="event">{{ user.profile.events[0].type }} : {{ user.profile.events[0].repo.name }}</div>
        </li>
    </ul>
</div>

angular.module('MyApp', [])

    .controller('DemoCtrl', function ($scope, SimpleGithubUser, AdvancedGithubUser) {

    $scope.users = [];

    $scope.fetchUsers = function () {
        $scope.users = [];
        var users = ['mhevery', 'igorminar', 'btford', 'substack', 'sindresorhus', 'n1k0', 'revolunet'];

        users.forEach(function (userName) {
            var user = new AdvancedGithubUser(userName);
            user.getProfile().then(function () {
                $scope.users.push(user);
            });
        });
    }
})

    .factory('SimpleGithubUser', function ($http) {
    var apiUrl = 'https://api.github.com/';

    // instantiate our object
    var SimpleGithubUser = function (username) {
        this.username = username;
        this.profile = null;
    };
    // this method will fetch data from GH API and return a promise
    SimpleGithubUser.prototype.getProfile = function () {
        // Generally, javascript callbacks, like here the $http.get callback, change the value of the "this" variable inside callbacks so we need ot keep a reference to the current instance "this", and we do it with the following :
        var self = this;
        return $http.get(apiUrl + 'users/' + this.username).then(function (response) {
            // we store the API result in user.profile. 
            self.profile = response.data
            // promises success should always return something in order to allow promise  chaining
            return response;
        });
    };
    return SimpleGithubUser;
})

// we inject our original service so we can extend it properly
.factory('AdvancedGithubUser', function ($http, SimpleGithubUser) {
    var apiUrl = 'https://api.github.com/';

    // instantiate our custom object with original object constructor
    var AdvancedGithubUser = function (username) {
        SimpleGithubUser.apply(this, arguments);
    };

    // duplicate the original object prototype
    AdvancedGithubUser.prototype = new SimpleGithubUser();

    // define a new internal method for this object
    function getUserEvents() {
        var self = this;
        return $http.get(apiUrl + 'users/' + this.username + '/events').then(function (response) {
            self.profile.events = response.data;
            return response;
        });
    }
    // we'll override our original getProfile
    AdvancedGithubUser.prototype.getProfile = function () {
        // first call the original getProfile method
        var originalGetProfile = SimpleGithubUser.prototype.getProfile.apply(this, arguments);
        // then once profile fetched, add some more user data
        var self = this;
        return originalGetProfile.then(function () {
            // call our private method, binding "this" to "self";
            return getUserEvents.call(self);
        });
    };
    return AdvancedGithubUser;
})

$line-height:40px;

button {
    font-size:22px;
    padding:10px;
}
* {
    font-family: 'Open Sans', sans-serif;
}
ul {
    padding: 10px;
}
li {
    background-color: darken(white, 2%);
    list-style-type: none;
    height:$line-height;
    padding:10px;
}
li.odd {
    background-color: darken(white, 5%);
}
img.gravatar {
    width:$line-height;
    height:$line-height;
    float:left;
    margin-right:10px;
}