Protractor Page Objects Inheritance

Given i'm building my angularjs protractor e2e tesing suite leveraging the page objects pattern. And i separate page object code in different files as much as reasonable. What would be a good approach to enable page objects inheritance? javascript classic inheritance? Object.create() based inheritance? Other? Should i keep expectations within the page object? Or favor Martin Fowler optinion by moving them to an assertion library? in which case how exactly would that look like in this javascript-nodejs technology stack? I've prepared a live jsfiddle playground here so you can try your improvements on. Or simply paste code within the answer, i'll paste the jsfiddle content below for clarity: loginPage.js ``` "use strict"; // A Page Object is a Singleton, so no need to constructors or classic js inheritance, // please tell me if I'm wrong or what's the utility of creating a (new LoginPage()) // every time a spec need to use this login page. var loginPage = { // Page Object Elements userElm: $('.user.loginPage'), // Page Object Assertions // Martin Fowler [doesn't favor](http://martinfowler.com/bliki/PageObject.html) // assertions in page objects, I'm open to suggestions on how to move // the assertions away from the Page Object and see how an assertion library // could like like in protractor. assertInputsDisplayed: function() { return ('Assertion: this.userElm: '+this.userElm); }, // Page Object Actions get: function () { return ('navigating to LoginPage with userElm: '+this.userElm); } }; module.exports.loginPage = loginPage; ``` loginDialog.js ``` "use strict"; var loginPage = require('./loginPage.js').loginPage; var helpers = require('./helpers.js'); // Inherit properties from another Page Object var loginDialog = helpers.extend({}, Object.create(loginPage), { // Page Object Elements userElm: $('.user.loginDialog'), // Page Object Actions get: function () { return ('navigating to LoginDialog with userElm: '+this.userElm); }, logout: function () { return ('logging out of Dialog. user was: '+this.userElm); } }); module.exports.loginDialog = loginDialog; ``` helpers.js ``` "use strict"; // some helper to avoid adding an external dependency for now var extend = function(target) { var sources = [].slice.call(arguments, 1); sources.forEach(function (source) { for (var prop in source) { target[prop] = source[prop]; } }); return target; }; ``` usage.js ``` "use strict"; // Mock $() for easy unit testing this on nodejs REPL global.$ = function(args) { return ('$BUILT '+args); }; var loginPage = require('./loginPage.js').loginPage; var loginDialog = require('./loginDialog.js').loginDialog; console.log(loginPage.userElm); //=> '$BUILT .user.loginPage' console.log(loginDialog.userElm); //=> '$BUILT .user.loginDialog' console.log(loginPage.get()); //=> 'navigating to LoginPage with userElm: $BUILT .user.loginPage' console.log(loginDialog.get()); //=> 'navigating to LoginPage with userElm: $BUILT .user.loginDialog' console.log(loginPage.assertInputsDisplayed()); //=> 'LoginPage assertion: this.userElm: $BUILT .user.loginPage' console.log(loginDialog.assertInputsDisplayed()); //=> 'LoginPage assertion: this.userElm: $BUILT .user.loginDialog' //loginPage.logout(); //=> TypeError: Object #<Object> has no method 'logout' console.log(loginDialog.logout()); //=> 'logging out of Dialog. user was: $BUILT .user.loginDialog' ```