In recent years a number of libraries for building large JavaScript applications has appeared. As we no longer need to battle DOM differences between browsers we can finally focus on building highly interactive front-end applications instead. But before we can do a good job with these new libraries we need unlearn our previous DOM-centric approach and need to be aware of good practices and patterns of developing modern javascript app. It will start with jQuery based old style practices and try to discuss on how can we approach to a modular, decoupled, scalable application architecture. This slide was prepared in very short time for technical session series of Digital World 2014 (http://www.digitalworld.org.bd/technical-session). The event video is here - https://www.youtube.com/watch?v=Gpw7l27MUUc (slide was not properly covered in video). It has taken inspiration, ideas (, even some contents) from the following sources - * http://addyosmani.com/largescalejavascript/ * http://addyosmani.com/resources/essentialjsdesignpatterns/book/ * https://www.youtube.com/watch?v=vXjVFPosQHw * https://www.youtube.com/watch?v=qWr7x9wk6_c * https://speakerdeck.com/kimjoar/patterns-of-large-scale-javascript-applications-1

1. Building Large Scale
Javascript Application
It's a little different than traditional JS

2. Who are the target audience?
What is Javascript?
I use JS to do form validation
Javascript is the interactive tool that I use for user intraction
I write the full app in JS

3. What do we actually mean by Large Scale Javascript
Application?
Large in size?
Large in complexity?
Large in developer count?

4. Why do we care?
The ability of browsers have increased
The load on the client, rather than on the server
High level of interaction

5. What is the secret of building BIG things?

6. Aircrafts are amazing architecture!

7. How they made this crazy huge thing?

8. The secret to building large apps is never build large
apps. Break up your applications into small pieces.
Then, assemble those testable, bite-sized pieces into
your big
– Justin Meyer

9. Okay, Let's start
As we generally start

10. We have a good main.js
function somethingGood() {
// Good code
}
// few other functions ...
$( document ).ready(function() {
$('#aButton').onClick(function(e) {
// Do something
});
// few event bindings ...
});

11. But at the end, it become bad!
function somethingGood() {
// ## Bad code, full of mess ##
}
// 39 strange functions with 40% repetation
$( document ).ready(function() {
$('#aButton').onClick(function(e) {
// Do something ## became 60 lines! ##
});
// ## 33 bindings ## , some event may bound multiple times
});

12. Let's break them down
Files++
Filesize--

13. Lots of files...
Let’s Organise them

14. By feature By Layer

15. By feature By Layer

16. Lets call them Modules

17. Okay, but...
What is a Module?

18. My Yahoo!

19. Modules made it!

20. Modules are (preferably) small, focused, purposeful
portion of code that -

21. Modules ... portion of code that -
Provides a specific feature

22. Modules ... portion of code that -
Contains business logic

23. Modules ... portion of code that -
Is decoupled (from other modules)

24. Modules ... portion of code that -
Is reusable (context matters)

25. Modules ... portion of code that -
Is testable

26. A simple module looks like -
var MyModule = ( function( window, $ ) {
function aPrivateMethod() {
$('catchSomething').load('http://...');
}
function myPublicMethod() {
privateMethod();
alert( 'my other method' );
}
// explicitly return public methods when this object is instantiated
return {
someMethod : myPublicMethod
};
} )( window, jQuery );

27. Module rules

28. Module Rule #1
Never access the DOM outside the module

30. Module Rule #2
Don't Create Global variables

31. Module Rule #3
Don’t Access Non-Native, Global objects

32. Module Rule #4
Inject Dependencies

33. Module Communation
with other modules

36. Mediator Pattern
Mediators are used when the communication between modules may be complex, but is still
well defined.

37. Mediators and Modules

38. Mediator publish/subscribe example
// example subscriber function
var Subscriber = function ExampleSubscriber( myVariable ) {
console.log( myVariable );
};
// example usages
var myMediator = new Mediator();
myMediator.subscribe( 'some event', Subscriber );
myMediator.publish( 'some event', 'foo bar' ); // console logs "foo bar"

40. Well defined Interfacing

41. Dependencies
Dependency on other code/Globals
Dependency on other files
Dependency on third party libraries

42. $('#my‐button').click(function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
});
Closure cannot be reused
Closure cannot be tested
$.get and $('#res') using global object

43. var downloadEmojis = function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
};
$('#my‐button').click(downloadEmojis);
Difficult to test
$.get and $('#res') using global object

44. var downloadEmojis = function(ajax, $el) {
ajax.get('https://api.github.com', function(data) {
$el.html(data.emojis_url);
});
};
$('#my‐button').click(function() {
downloadEmojis($, $('#res'));
});
Now we can controle dependencies :)

45. Dependency on other files/Modules

46. Scripts behind this presentation
<script src="bower_components/bespoke.js/dist/bespoke.min.js"></script>
<script src="bower_components/bespoke‐keys/dist/bespoke‐keys.min.js"></script>
<script src="bower_components/bespoke‐touch/dist/bespoke‐touch.min.js"></script>
<script src="bower_components/bespoke‐bullets/dist/bespoke‐bullets.min.js"></script>
<script src="bower_components/bespoke‐scale/dist/bespoke‐scale.min.js"></script>
<script src="bower_components/bespoke‐hash/dist/bespoke‐hash.min.js"></script>
<script src="bower_components/bespoke‐progress/dist/bespoke‐progress.min.js"></script>
<script src="bower_components/bespoke‐state/dist/bespoke‐state.min.js"></script>
<script src="bower_components/prism/prism.js"></script>
<script src="bower_components/prism/components/prism‐php.min.js"></script>
<script src="scripts/main.js"></script>

47. How can we make it better?
AMD
COMMON.JS

48. Let's see a little bit more about AMD
Using require.js

49. Using require.js
Include Require JS
<script data‐main="scripts/main" src="scripts/require.js"></script>

50. Using require.js
Configure Paths
require.config({
baseUrl: 'js/lib',
paths: {
jquery: 'jquery‐1.9.0'
parse : 'parse‐1.2.18.min',
underscore: 'underscore',
backbone: 'backbone',
marionette: 'backbone.marionette'
}
});

51. Using require.js
Define modules
define([
'app',
'marionette'
], function(app, Marionette){
return ExampleModule = app.module("Example", function(Example) {
this.startWithParent = false;
this.addInitializer(function(){
console.log('Module:Example => initialized');
this.router = new Router({ controller: Controller });
});
});
});

52. Asynchronous loading

53. On demand script loading
if(teamProfile) {
// Load and show team profile
require(['views/TeamProfileView'], function(TeamProfileView) {
var teamInfo = { model : app.reqres.request('core:team', shortName) }
app.main.show(new TeamProfileView(teamInfo));
});
}

54. Dependency on third party libraries

55. http://bower.io/

56. list dependencies in bower.json
// bower.json
{
"dependencies": {
"angular": "~1.0.7",
"angular‐resource": "~1.0.7",
"jquery": "1.9.1"
} }

57. MV* Frameworks

58. Seperation between Data and DOM
M → Data | V → DOM | * → has many variations

59. MVC
Controller → Mediates inputs and manipulates the model

60. MVP
Presenter → all presentation logic is pushed to the presenter

61. MVVM
ViewModel → exposes model so it can be easily managed and consumed

62. How to select the right one?
Why they are this huge in nymbers? :(

63. Same todo app built around 70 times with different frameworks and approaches

65. Let's see how BackboneJS did it

66. Todo Model
(function () {
app.Todo = Backbone.Model.extend({
// and ensure that each todo created has `title` and `completed` keys.
defaults: {
title: '',
completed: false
},
toggle: function () {
this.save({
completed: !this.get('completed')
});
}
});
})();

67. Create a Todo
var todo = new app.Todo({
title: "Do something good!"
});

68. What about list of Todos?
var Todos = Backbone.Collection.extend({
model: app.Todo,
// Filter down the list of all todo items that are finished.
completed: function () {
return this.filter(function (todo) {
return todo.get('completed');
});
},
// Many other functions related to list ...
});
Collections

69. Create a Todo list
var todoList = new Todos(
{title: 'Do something good'},
{title: 'Another Task'},
{title: 'This task is Done', completed: true},
);

70. Who will create them actually?
collection.fetch(); // Pulls list of items from server
collection.create(); // Create new item in list
// Sync a model
model.fetch(); // Fetch an item from server
model.save(); // Save changes to model
model.destroy(); // Delete a model

71. Template
<script type="text/template" id="item‐template">
<div class="view">
<input class="toggle" type="checkbox" <%= completed ? 'checked' : '' %>>
<label><%= title %></label>
<button class="destroy"></button>
</div>
<input class="edit" value="<%‐ title %>">
</script>
The DOM to render models or collection

72. Views
app.TodoView = Backbone.View.extend({
tagName: 'li',
template: _.template($('#item‐template').html()),
initialize: function () {
this.listenTo(this.model, 'change', this.render);
this.listenTo(this.model, 'visible', this.toggleVisible);
},
render: function () {
this.$el.html(this.template(this.model.toJSON()));
return this;
}
});
Takes models, Render them, listning to events

73. Views cont.
events: {
'click .toggle': 'toggleCompleted',
'dblclick label': 'edit'
},
toggleCompleted: function () {
this.model.toggle();
},
edit: function () {
this.$el.addClass('editing');
this.$input.focus();
},
Handling to DOM events and manipulate model

74. Routers
var TodoRouter = Backbone.Router.extend({
routes: {
'*filter': 'setFilter',
'url/pattern': 'handlerFunction'
'url/pattern/:param': 'handlerFunction'
},
setFilter: function (param) {
// Trigger a collection filter event
app.todos.trigger('filter');
}
});
Handles the routing with url changes

75. Start listning to url changes
app.TodoRouter = new TodoRouter();
Backbone.history.start();

76. Url change? reload?... NO
http://the/app/url.com#a‐route
http://the/app/url.com#another‐route
http://the/app/url.com#a‐route/withParam/23

77. No more today
It was a lot of things... ain't it?

78. Wait... Do I really need aaall of these?
Well, depends on your apps requirement

79. Resource
http://superherojs.com/

80. About us
[
{
"name": "Mohammad Emran Hasan",
"mail": "phpfour@gmail.com",
"blog": "http://emranhasan.com"
},
{
"name": "Anis Uddin Ahmad",
"mail": "anisniit@gmail.com",
"blog": "http://ajaxray.com"
}
]

81. Questions?