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of
large-scale JavaScript applications
patters
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Kim Joar Bekkelund
I work here
@kimjoar <- Twitter
@kjbekkelund <- GitHub
kimjoar.net
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We’re going to talk about
large JavaScript apps
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We’re going to talk about
large JavaScript apps
where “large”
really doesn’t need
to be that large
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Most of this will apply to the
JavaScript apps we write
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$('#my-button').click(function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
});
we always start with a small feature …
The problem with JavaScript is that
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suddenly 5k lines in one file
“how did this happen?”
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Unobtrusive JavaScript
cirka 2006
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Unobtrusive JavaScript +
cirka 2006
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$
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$
DOM MANIPULATION
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$
$.fn.everything
$(“.test”).parent().parent();
DOM MANIPULATION
$(document).ready(everything)
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$
DOM MANIPULATION
Too often, the business logic is hidden in a mess of code
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jQuery(document).ready(function() {
$(".user form").submit(function(e) {
e.preventDefault();
$.ajax({
// ...
success: function(data) {
var name = data.name || "Unknown";
$(".user .info").append("
" + name + "
"); } }) }); });Slide 16
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jQuery(document).ready(function() {
$(".user form").submit(function(e) {
e.preventDefault();
$.ajax({
// ...
success: function(data) {
var name = data.name || "Unknown";
$(".user .info").append("
" + name + "
"); } }) }); }); Page event User event Network I/O Network event Parsing response Templating Callback hell https://speakerdeck.com/bkeepers/the-plight-of-pinocchioSlide 17
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Considerable increase in
the amount of JavaScript
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Complex Single page apps
now
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backend --> frontend
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New capabilities:
geolocation, local storage,
canvas, web workers, WebSockets
backend --> frontend
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The biggest problem is no longer the browser
it’s the size and complexity of our apps
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We want
testable, scalable, maintainable
JavaScript
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This is difficult!
actually
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we need to unlearn
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we need to unlearn our DOM-centric approach
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we need to unlearn our DOM-centric approach
The DOM is Inherently global and stateful
hard to test and maintain
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we need to unlearn how we write JavaScript
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we need to unlearn how we write JavaScript
No more 5k lines of code in a single file
Watch out for global variables
Learn from the backend
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we need to unlearn how we use jQuery
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we need to unlearn how we use jQuery
“Our experience is that, when code is
difficult to test, the most likely cause is
that our design needs improving.”
– Growing Object-Oriented Software, Guided by Tests
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– Justin Meyer
“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
application.”
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There’s so much choice
that you end up feeling like
this guy
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There’s so much choice
that you end up feeling like
this guy
We need a foundation
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we need to move state
away from the DOM
most importantly
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MVC
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MVC Google Trends for
“JavaScript mvc”
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MVC
A clean separation between data and the DOM
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MVC
Mediates inputs and
manipulates the model
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MVC
NOT THE ONLY ONE.
MANY VARIATIONS.
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MV*
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MV*
everyone has a
different take
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MVP
all presentation logic is
pushed to the presenter
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MVVM
exposes model so it can be easily
managed and consumed
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“I hereby declare AngularJS to be MVW
framework – Model-View-Whatever.
Where Whatever stands for ‘whatever
works for you’.”
– Igor Minar
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The most important aspect is
to separate STATE and the DOM
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First step ✓
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However,
MV* is not enough
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“Lots of monolithic single
files that contained too
much code.”
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“Actually how you partition your
code has a lot to do with how you
organize your project source code
and how much easier it is to
maintain as your project grows.”
– Jim Lavin
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# files ++
filesize --
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Package by feature Package by layer
vs
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Package by feature Package by layer
vs
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Package by feature
I prefer
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Package by feature
I prefer
I call them Modules
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Module
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Module
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Module
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Modules
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Modulescontain business logic
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Modules small
are
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Modules focused
are
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Modulesare decoupled
from other modules
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Modulesare preferably reusable
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Modulesare easily testable
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“A system is easier to change if its
objects are context-independent;
that is, if each object has no built-in
knowledge about the system in
which it executes.”
– Growing Object-Oriented Software, Guided by Tests
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Module rules
http://www.slideshare.net/nzakas/scalable-javascript-application-architecture-2012
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Module rules
Never access the DOM
outside the module
http://www.slideshare.net/nzakas/scalable-javascript-application-architecture-2012
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Module rules
Never access the DOM
outside the module
Don’t create
global variables
http://www.slideshare.net/nzakas/scalable-javascript-application-architecture-2012
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Module rules
Never access the DOM
outside the module
Don’t create
global variables
Don’t access global,
non-native objects
http://www.slideshare.net/nzakas/scalable-javascript-application-architecture-2012
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Keeping this in mind
should get you a long way
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Next up: dependencies
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We depend on other code
dependencies
We depend on other files
We depend on Third-party libraries
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We depend on other code
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We usually depend far
too much on globals
We depend on other code
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We usually depend far
too much on globals
JavaScript makes
this really easy
We depend on other code
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$('#my-button').click(function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
});
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$('#my-button').click(function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
});
Cannot be reused
Globals
DIFFICULT TO TEST
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var downloadEmojis = function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
};
$('#my-button').click(downloadEmojis);
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var downloadEmojis = function() {
$.get('https://api.github.com', function(data) {
$('#res').html(data.emojis_url);
});
};
$('#my-button').click(downloadEmojis);
Globals
DIFFICULT TO TEST
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var downloadEmojis = function(ajax, $el) {
ajax.get('https://api.github.com', function(data) {
$el.html(data.emojis_url);
});
};
$('#my-button').click(function() {
downloadEmojis($, $('#res'));
});
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var downloadEmojis = function(ajax, $el) {
ajax.get('https://api.github.com', function(data) {
$el.html(data.emojis_url);
});
};
$('#my-button').click(function() {
downloadEmojis($, $('#res'));
});
Now we can control the dependencies
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var UserView = function(el, user) {
this.el = el;
this.user = user;
};
// let's just create a super simple user object
var user = {
image: 'http://example.com/image.png'
};
// initialize with the element the view owns and a user
var view = new UserView($('.user'), user);
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var UserView = function(el, user) {
this.el = el;
this.user = user;
};
UserView.prototype.showImage = function() {
this.el.append('
');
};
// let's just create a super simple user object
var user = {
image: 'http://example.com/image.png'
};
// initialize with the element the view owns and a user
var view = new UserView($('.user'), user);
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var UserView = function(el, user) {
this.el = el;
this.user = user;
};
UserView.prototype.showImage = function() {
this.el.append('');
};
// let's just create a super simple user object
var user = {
image: 'http://example.com/image.png'
};
// initialize with the element the view owns and a user
var view = new UserView($('.user'), user);
// ... and now we can do stuff which changes the DOM
view.showImage();
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Always inject dependencies
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has embraced this
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var MyController = function($scope, $http) {
$http.get('https://api.github.com')
.success(function(data) {
$scope.emojis_url = data.emojis_url;
});
}
An example using AngularJS
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var MyController = function($scope, $http) {
$http.get('https://api.github.com')
.success(function(data) {
$scope.emojis_url = data.emojis_url;
});
}
the ordering of these does not matter
An example using AngularJS
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var MyController = function($http, $scope) {
$http.get('https://api.github.com')
.success(function(data) {
$scope.emojis_url = data.emojis_url;
});
}
the ordering of these does not matter
An example using AngularJS
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// Create an AngularJS module with no dependencies
var ndc = angular.module('ndc', []);
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// Create an AngularJS module with no dependencies
var ndc = angular.module('ndc', []);
// Register a function
ndc.factory('awesome', function() {
return 'awesome conference';
});
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// Create an AngularJS module with no dependencies
var ndc = angular.module('ndc', []);
// Register a function
ndc.factory('awesome', function() {
return 'awesome conference';
});
// Get the injector (happens behind the scenes in AngularJS apps)
var injector = angular.injector(['ndc', 'ng']);
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// Create an AngularJS module with no dependencies
var ndc = angular.module('ndc', []);
// Register a function
ndc.factory('awesome', function() {
return 'awesome conference';
});
// Get the injector (happens behind the scenes in AngularJS apps)
var injector = angular.injector(['ndc', 'ng']);
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// Create an AngularJS module with no dependencies
var ndc = angular.module('ndc', []);
// Register a function
ndc.factory('awesome', function() {
return 'awesome conference';
});
// Get the injector (happens behind the scenes in AngularJS apps)
var injector = angular.injector(['ndc', 'ng']);
// Call a function with dependency injection
injector.invoke(function(awesome) {
console.log('awesome() == ' + awesome);
});
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// Create an AngularJS module with no dependencies
var ndc = angular.module('ndc', []);
// Register a function
ndc.factory('awesome', function() {
return 'awesome conference';
});
// Get the injector (happens behind the scenes in AngularJS apps)
var injector = angular.injector(['ndc', 'ng']);
// Call a function with dependency injection
injector.invoke(function(awesome) {
console.log('awesome() == ' + awesome);
});
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http://docs.angularjs.org/guide/dev_guide.templates.databinding
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http://docs.angularjs.org/guide/dev_guide.templates.databinding
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{{#if isExpanded}}
{{body}}
Contract
{{else}}
Show More...
{{/if}}
App.PostController = Ember.ObjectController.extend({
body: 'body',
isExpanded: false,
expand: function() {
this.set('isExpanded', true);
},
contract: function() {
this.set('isExpanded', false);
}
});
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{{#if isExpanded}}
{{body}}
Contract
{{else}}
Show More...
{{/if}}
App.PostController = Ember.ObjectController.extend({
body: 'body',
isExpanded: false,
expand: function() {
this.set('isExpanded', true);
},
contract: function() {
this.set('isExpanded', false);
}
});
no jquery!
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dependencies
We depend on other code
We depend on other files
We depend on Third-party libraries
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We depend on other files
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The order of elements
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The order of elements
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The order of elements
Lots of globals Weakly stated dependencies
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CommonJS AMD
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CommonJS AMD
var $ = require('jquery');
exports.myFn = function () {};
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CommonJS AMD
var $ = require('jquery');
exports.myFn = function () {};
define(['jquery'] , function ($) {
return function () {};
});
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CommonJS AMD
var $ = require('jquery');
exports.myFn = function () {};
define(['jquery'] , function ($) {
return function () {};
});
works better in current browsers
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AMD
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dependencies
We depend on other code
We depend on other files
We depend on Third-party libraries
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We depend on Third-party libraries
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Package manager
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Bower
// bower.json
{
"dependencies": {
"angular": "~1.0.7",
"angular-resource": "~1.0.7",
"jquery": "1.9.1"
}
}
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Bower
// bower.json
{
"dependencies": {
"angular": "~1.0.7",
"angular-resource": "~1.0.7",
"jquery": "1.9.1"
}
}
$ bower install
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… and that’s as far as we’ll go today
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is all of this necessary?
… but seriously,
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Want to learn more?
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Questions?