JavaScript Patterns and Principles

© 2013 Adobe Systems Incorporated. All Rights Reserved.© 2013 Adobe Systems Incorporated. All Rights Reserved.
JavaScript Patterns And Principles
Aaron Hardy | Software Engineer, Analytics

© 2013 Adobe Systems Incorporated. All Rights Reserved.
Architecture Misconceptions
2
jQuery is
my architecture.

3
jQuery is
my architecture.
Websites are
just the V in MVC.

4
jQuery is
my architecture.
Websites are
just the V in MVC.
We’re already using
MVC so we’re good.

5
jQuery is
my architecture.
Websites are
just the V in MVC.
We’re already using
MVC so we’re good.

§  Modularity
§  Communication Patterns
§  Patterns Within MV*
6

§  Modularity
7

Building Large Apps
8
The secret to building large apps is NEVER
build large apps. Break your application
into small pieces. Assemble those testable,
bite-sized pieces into your application.
- Justin Meyer

Modules Should Be…
9
Independent
of other modules

10
Independent
of other modules
Limited knowledge
of the rest of the app

11
Independent
of other modules
Reusable
without refactoring
Limited knowledge

12
Independent
of other modules
Reusable
without refactoring
Limited knowledge
Functional
when other modules break

13
Independent
of other modules
Testable
in isolation
Reusable
without refactoring
Limited knowledge
Functional
when other modules break

Possible Modules
Feed
Address Book
Chat Room
Menu
Shared Service
14

§  Modularity
§  Callback
§  Promise
§  Event Emitter
§  Publish/Subscribe
15

§  Modularity
§  Callback
§  Promise
16

Callbacks In Real Life
§  TODO: Picture of a fast food line while I explain how it demonstrates callbacks in real life.
17
CC Image Courtesy of The Consumerist on Flickr

Callback Example
var customer = {
placeOrder: function() {
restaurant.takeOrder('burger', this.onFoodReady);
},
onFoodReady: function(food) { … }
};
18

Callback Example
var customer = {
placeOrder: function() {
restaurant.takeOrder('burger', this.onFoodReady);
},
onFoodReady: function(food) { … }
};
var restaurant = {
takeOrder: function(order, foodReadyCallback) {
// call foodReadyCallback(food) when food is ready
}
};
19

Callback Key Points
Used to notify of completion of an asynchronous task
Simple
Eﬃcient
No libraries required
20

§  Modularity
§  Callback
§  Promise
21

Promises In Real Life
22

jQuery Promise Anatomy
23
takeSeatingRequest()
promise Promise
then()
Customer Restaurant

jQuery Promise Anatomy
24
takeSeatingRequest()
promise
Deferred
resolve()
reject()
promise()
Promise
then()
Customer Restaurant

Promise Example
var customer = {
requestSeating: function() {
var promise = restaurant.takeSeatingRequest();
promise.then(this.sit);
}
sit: function() { … }
};
25

Promise Example
var customer = {
}
sit: function(table) { … }
};
var restaurant = {
takeSeatingRequest: function() {
var deferred = $.Deferred();
setTimeout(function() {
deferred.resolve({seats: 4});
}, 5000);
return deferred.promise();
}
};
26

Promise Example
var customer = {
promise.fail(this.leave);
}
sit: function(table) { … },
leave: function() { … }
};
var restaurant = {
takeSeatingRequest: function() {
var deferred = $.Deferred();
deferred.reject(); // Sorry, we’re closed!
return deferred.promise();
}
};
27

Asynchronous Sequence Using Callbacks
step1(function(value1) {
step2(value1, function(value2) {
console.log('Success', value4);
}
}
}
}
28

Asynchronous Sequence Using Callbacks
step1(function(value1) {
console.log('Success', value4);
}
}
}
}
29
PYRAMID OF DOOM

Asynchronous Sequence Using Promises
step1()
.then(step2)
.then(step3)
.then(step4)
.then(function(value) {
console.log('Success', value);
});
30
Supported in jQuery 1.8+

Try-catch In A Synchronous World
try {
var value = step1();
value = step2(value);
} catch (error) {
console.log('Failure', error);
} finally {
console.log('Time to clean up resources!');
}
31

Asynchronous Try-catch Using Promises
step1()
.then(step2)
.then(step3)
.then(step4)
.then(function(value) {
})
.catch(function(error) {
console.log('Failure', error);
})
.finally(function() {
console.log('Time to clean up resources!');
});
32
Supported in the Q promise library

Asynchronous Parallel Using Callbacks
var requestsPending = 2;
var onComplete = function(tweets) {
requestsPending--;
if (requestsPending == 0) {
// Display tweets from both requests.
}
}
loadTweets('#adobe', onComplete);
loadTweets('#summit', onComplete);
33

Asynchronous Parallel Using Callbacks
var requestsPending = 2;
var onComplete = function(tweets) {
requestsPending--;
if (requestsPending == 0) {
// Display tweets from both requests.
}
}
loadTweets('#adobe', onComplete);
loadTweets('#summit', onComplete);
34
o_O

Asynchronous Parallel Using Promises
var adobePromise = loadTweets('#adobe');
var summitPromise = loadTweets('#summit');
$.when(adobePromise, summitPromise).then(displayTweets);
35

Promise Key Points
Used to notify of completion of an asynchronous task
Object passable now representing something to be determined in the future
Great for sequential/parallel management
Generally makes use of a third party library
36

§  Modularity
§  Callback
§  Promise
37

Event Emitters In Real Life
§  TODO: Coupon text photo while I explain the similarities to event emitters.
38
CC Image Courtesy of Incase on Flickr

DOM Event Emitter Example
var foo = document.getElementById('foo');
foo.addEventListener('click', function() {
alert('bar');
});
foo.addEventListener('click', function() {
alert('baz');
});
39

jQuery Event Emitter Example
var customer = {
receiveCoupon: function(coupon) { … }
};
40

var customer = {
};
var restaurant = {
offerCoupon: function(coupon) {
$(this).trigger('couponAvailable', coupon);
}
};
41

var customer = {
};
var restaurant = {
offerCoupon: function(coupon) {
$(this).trigger('couponAvailable', coupon);
}
};
$(restaurant).on('couponAvailable', customer.receiveCoupon);
42

Event Emitter Key Points
Notifies of state change, user interaction, etc.
Fires an event any number of times (possibly never)
Native for DOM
Arbitrary objects make use of a third-party library
43

§  Modularity
§  Callback
§  Promise
§  Patterns within MV*
44

Pub/Sub Anatomy
45
Pub/Sub Bus
publish()
subscribe()
unsubscribe()

Pub/Sub Anatomy
46
Pub/Sub Bus
publish()
subscribe()
unsubscribe()
Customer
bus.subscribe('couponAvailable', function() { … });

Pub/Sub Anatomy
47
Pub/Sub Bus
publish()
subscribe()
unsubscribe()
RestaurantCustomer
bus.publish('couponAvailable', 'Buy 1 get 1 free');

Pub/Sub Example
48
Archive Report spam Delete Mark as unread
Android 4.2.1 vs iOS 6
Videos magically don’t have sound
If you could scale this to market it would be very valuable, no?
Clone SSD (Windows system partition) to HDD partition
JIRA help – Greenhopper + Scrum + Subtasks
Question setting up a VPN on firewall
Shopping Carts
The end of textbooks?
3MeMail

Pub/Sub Example
49
Shopping Carts
0MeMail
Inbox
Service

Pub/Sub Example
50
Shopping Carts
3MeMail
Mark all as read

Pub/Sub Example
51
Shopping Carts
3MeMail
bus.publish('selectedEmailsChanged', selectedEmails);
Bus
Mark all as read

Pub/Sub Example
52
Shopping Carts
3MeMail
Archive Report spam Delete Mark as read

Pub/Sub Example
53
Shopping Carts
3MeMail
Bus
Service
bus.publish('markAsReadRequested', emails);

Pub/Sub Example
54
Shopping Carts
3MeMail
Bus
Service
bus.publish('markedAsRead', emails);

Pub/Sub Example
55
Shopping Carts
2MeMail

Pub/Sub Key Points
Communication between modules
Publishers and subscribers don’t address one another
Provides excellent decoupling
56

Which Pattern Should I Use?
57
Is the communication
between modules?
Is it communicating
a response to requested task?
Do you need to represent
a future value?
Is sequence/parallel
management important?
No Yes
No Yes
No YesEvent Emitter
Callback Promise
Pub/Sub

§  Modularity
§  State Change Detection
§  Declarative Markup
§  View Manipulation
§  Dependency Injection
58

MVC
59
Model
Represents data
or state
View
Presentation and
user controls
Controller
Logic between views
and models

MVP
60
Model
Represents data
or state
View
Presentation and
user controls
Presenter
Logic between views
and models

MVVM
61
Model
Represents data
or state
View
Presentation and
user controls
ViewModel
Logic between views
and models

MV*
62
Model
Represents data
or state
View
Presentation and
user controls
*

MV* Frameworks
63

Comparison At A Glance
64
Requires Underscore/LoDash and jQuery/Zepto
6K + 4K (Underscore) + 28K (jQuery 2.0) gzipped
Non-prescriptive
Extensions add functionality and/or prescription
Eventful proxy models
Used in tandem with a template engine
Binding available through extensions
Dependency injection available through extensions
jqLite built-in
29K gzipped
Prescriptive
Intended to be a full(er) stack out of the box
Dirty checking
Custom HTML tags and attributes (directives)
Two-way data-binding built-in
Dependency injection built-in

§  Modularity
§  State Change detection
65

Backbone: Proxy Models
66
var book = {
title: 'A Tale of Two Cities',
author: 'Charles Dickens',
genre: 'Historical',
};
var bookView = new BookView(book);
book.genre = 'Social Criticism';
How does BookView know
that the book’s genre changed?

67
var book = {
};
bookView.genreChanged(); We could manually tell it…

68
var book = {
};
bookView.genreChanged(); We could manually tell it…
but not without creating
a tangled mess.

69
Let’s wrap our object
in a proxy.
var book = new Backbone.Model({
});
book.set({genre: 'Social Criticism'}); Now we must use the
proxy functions.
(Until ECMAScript Harmony!)

70
Meanwhile, inside BookView…
book.on('change:genre', onChange);
var book = new Backbone.Model({
});
book.set({genre: 'Social Criticism'});

71
We do something similar for
arrays.
var books = new Backbone.Collection([
book1,
book2,
book3
]);
var booksView = new BooksView(books);
books.add(book4);
books.on('add', onAdd);

Angular: Dirty Checking
72
Meanwhile inside BookView…
var book = {
};
…pass book to BookView…
$scope.book = book;
$scope.$watch('book', function() {
console.log('changed!');
}, true);

Angular: Dirty Checking
73
User Click
Change Object
Watchers: Is the
object diﬀerent
than last time?
Yes. React.
Watchers: Is the
object diﬀerent
than last time?
No
Digest Cycle
Triggered automatically
on user interaction,
http responses, etc.
Can be manually triggered.
TriggerWait

§  Modularity
74

Backbone: Templates
<script id="users-template"
type="text/x-handlebars-template">
<ul>
{{#users}}
<li>Name: {{name}}, Email: {{email}}</li>
{{/users}}
</ul>
</script>
75

Backbone: Templates
var data = {
users: [
{ name: 'John', email: 'john@example.com' },
{ name: 'Jane', email: 'jane@example.com' }
]
};
var source = $('#users-template').html();
var template = Handlebars.compile(source);
var html = template(data);
$('body').html(html);
76

Backbone: Templates
<body>
<ul>
<li>Name: John, Email: john@example.com</li>
<li>Name: Jane, Email: jane@example.com</li>
</ul>
</body>
77

Angular: Directives
<ul>
<li ng-repeat="user in users">
Username: {{user.name}}, Email: {{user.email}}
</li>
</ul>
function MyController($scope) {
$scope.users = [
{name: 'John', email: 'john@example.com'},
{name: 'Jane', email: 'jane@example.com'}
];
}
78

§  Modularity
79

Backbone: Responding To And Updating View
Name: <input type="text" class="name-in">
<h1>Hello <span class="name-out"></span></h1>
Backbone.View.extend({
events: {
'keyup .name-in': 'onNameChange'
},
onNameChange: function(event) {
// TODO: Optimize
var name = $(event.target).val();
this.$('.name-out').text(name);
}
});
80

Angular: Binding
Name: <input type="text" ng-model="yourName">
<h1>Hello {{yourName}}</h1>
81

§  Modularity
§  State change detection
82

Without Dependency Injection
83
var TweetStream = function() {
this.twitter = new TwitterService();
};
TweetStream.prototype.showTweets = function() {
var tweets = this.twitter.getTweets();
…
};
var stream = new TweetStream();
stream.showTweets();

With Dependency Injection
84
var TweetStream = function(twitter) {
this.twitter = twitter;
};
TweetStream.prototype.showTweets = function() {
var tweets = this.twitter.getTweets();
…
};
var twitter = new TwitterService();
var stream = new TweetStream(twitter);
stream.showTweets();
We inverted control of the
TwitterService construction.

Inversion of Control Container
When rank is requested, provide the value 1337.
When twitter is requested, provide a new instance of TwitterService.
When dialog is requested, provide the SearchDialog constructor.
When logger is requested, provide a singleton instance of AsyncLogger.
When chat is requested, provide whatever is returned from chatFactory.
85

Angular: Dependency Injection
86
var MyController = function($http, $scope) {
$http.get('http://github.com/…')
.success(function(commits) {
$scope.commits = commits;
});
};
$injector.instantiate(MyController);
How does $injector know
what to inject for $http
and $scope?

87
});
};
How does $injector know
what to inject for $http
and $scope?
By using toString() and
some well-crafted regex.

88
});
};
What if we reverse the
parameter order?

89
var MyController = function($scope, $http) {
});
};
parameter order?
It still works!

90
var MyController = function(a, b) {
a.get('http://github.com/…')
.success(function(c) {
b.commits = c;
});
};
parameter order?
It still works!
Until we minify it.

91
var MyController = function(a, b) {
a.get('http://github.com/…')
.success(function(c) {
b.commits = c;
});
};
MyController.$inject = ['$http', '$scope'];
parameter order?
It still works!
Until we minify it.
Then we have to annotate.

§  Modularity
92

Promise Implementations
93
Q
jQuery
rsvp.js
kriskowal/q
jquery/jquery
tildeio/rsvp.js

Pub/Sub Implementations
94
Postal.js
AmplifyJS
PubSubJS
postaljs/postal.js
appendto/amplify
mroderick/pubsubjs

Inversion of Control and Dependency Injection
95
Article by Martin Fowler
http://martinfowler.com/articles/injection.html
Wikipedia source of truth
http://en.wikipedia.org/wiki/Dependency_injection
Lightweight inversion of control container with examples
https://github.com/Aaronius/injectorjs

Inversion of Control and Dependency Injection
96
Article by Martin Fowler
http://martinfowler.com/articles/injection.html
Wikipedia source of truth
http://en.wikipedia.org/wiki/Dependency_injection
Lightweight inversion of control container with examples
https://github.com/Aaronius/injectorjs

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