A Lecture given in Aalto University course "Design of WWW Services". Single page app is already several years old web application paradigm that is now gaining traction due to the interest towards HTML5 and particularly cross-platform mobile (web) applications. The presentation overviews the single page application paradigm and compares it with other web app paradigms. The presentation uses Backbone.js as the sample and gives practical tips on how to best structure Backbone.js applications. It contains an extensive set of tips and links in the notes section. The reader is adviced to download the presentation for better readability of the notes.

1. Building Single-page
Applications
HTML5 expertise at your service

2. About Lauri & SC5 Online
• ”Powerhouse for software projects”
• HUT graduate, Information Networks
• 15 years in software engineering business
• A few startups & corporations behind
• Now in SC5 Online as a Software Architect
• Specializes in HTML5 application development
• Located in Helsinki (Kamppi) + Jyväskylä (Innova 2)
• Founded in 2006, employs 50 people
• Customers e.g. Sanoma, YLE, Veikkaus, F-Secure
• blog.sc5.io, twitter: @sc5io

3. Single-page Application
A web application or web site that fits on a single web page with the
goal of providing a more fluid user experience akin to a desktop
application.
Wikipedia

5. Single-page Application
Single page apps typically have
– “application like” interaction
– dynamic data loading from the server-side API
– fluid transitions between page states
– more JavaScript than actual HTML
They typically do not have
– support for crawlers (not for sites relying on search traffic)
– support for legacy browsers (IE7 or older, dumbphone
browsers)

6. SPAs Are Good For …
• “App-like user experience”
• Binding to your own (or 3rd party) RESTful API
• Replacement for Flash or Java in your web pages
• Hybrid (native) HTML5 applications
• Mobile version of your web site
The SPA sweet spot is likely not on web sites,
but on content-rich cross-platform mobile apps

7. App-like User Experience
Note: These (all) are not our work but showcases that Finns can do good stuff!

8. Native Apps vs. Hybrid/Mobile Web Sites
“The real problem with apps was that when people read on electronic
media, they expect the stories to possess the linky-ness of the Web—
but stories in apps didn’t really link.”
“Software development of apps was much harder than publishers had
anticipated, because they had hired Web developers who knew
technologies like HTML, CSS, and JavaScript. Publishers were
astonished to learn that iPad apps were in fact real, if
small, applications, written mostly in a language called Objective
C, which no one in their Web-dev departments knew. Publishers
responded by outsourcing app development, which was
expensive, time-consuming, and unbudgeted.”
Why Publishers Don't Like Apps in MIT Technology Review

9. SPAs and Other Web App Architectures
Server-side Server-side + AJAX PJAX SPA
What Server round-trip on Render initial page on Render initial page on Serve static page
every app state change server, state changes server, state changes skeleton from server;
on the client on server, inject into render every change on
DOM on client-side client-side
How UI code on server; links UI code on both ends; UI code on server, UI code on client,
& form posting AJAX calls, ugly server client to inject HTTP, server API
API server API if you like
Ease of development
UX & responsiveness
Robots & old browsers
Who’s using it? Amazon, Wikipedia; Facebook?; Twitter, Basecamp, Google+, Gmail, FT;
banks, media sites etc. widgets, search GitHub mobile sites, startups

10. SPA Frameworks
Need help in comparison? Try TodoMVC!

11. Anatomy of a Backbone SPA
• Application as a „singleton‟
reference holder
• Router handles the navigation and
toggles between views
• Models synchronize with Server
API
• Bulk of the code in views
• All HTML in templates

12. SPA Client-Server Communication
• HTML and all the assets are loaded in
first request
• Additional data is fetched over
XMLHTTPRequest
• In addition to normal server stack, you
need to have API endpoints in the same
level as presentation layer
• If you want to go real-time, WebSockets
(socket.io) can help you
• When it gets slow, cluster the backend
behind a caching reverse proxy like
Varnish

13. Sample App Stack
App
Backbone App When the app gets complex, you need modularity
(Backbone Router)  require.js
Views Models
Router (Backbone View) (Backbone Model)
(Backbone Router) When the devices have differences, you need
feature detection (only a few shims really work)
modernizr
(feature
Backbone
LayoutManager
Handlebars  modernizr, semantic.gs
(template engine)
detection) (view utility)
DOMReady
fastclick
(normalise
(bootstrapping) View & Templating Stack When you want to have an optimized app,
click handling)
Underscore.js
(object/array
Backbone variability or a native app, you need builds
 grunt
(MVC framework)
utils)
Cross-Browser jQuery
Compatibility Utility Belt (DOM access)
RequireJS
(dependency mgmt)
Sample boilerplate available at SC5 GitHub
320 and Up Semantic.gs
(boilerplate) HTML5 Foundation (boilerplate)
Our component
Bower LESS Jasmine Grunt Node.js & Express
(package mgmt) (CSS) (unit tests) (builds) (web/API server) 3rd party component
Build, Testing & Deployment Subsystems

14. Handling Navigation (location)
• Browsers already have navigation controls; support them
• HTML5 pushState exists exactly for this purpose
• Handled by History in Backbone and $location in Angular
• Remember fallback to hashbang „#‟ with legacy browsers
• Remember to use URL rewrites in the server side

15. Handling Models (dynamic data)
• Backbone has a flat model of Collections containing Models
• Input validation (can block the invalid input, blocks on save())
• Multiple view bindings (through events)
• Custom data - model mappings (through parse())
• Synchronizing with servers
• fetch() -> GET
• save() -> POST or PUT
• delete() -> DELETE

16. Handling Models (dynamic data)
• Can be easily extended by overriding Backbone.sync()
• Real-time communications (web sockets)
• Offline use (localStorage)
• Avoid spaghetti code:
• If your UI state does not fit the server schema, override parse()
and save()
• Use the models as the state of your views
• Isolate client-server communication to models and collections
• If you ever plan to reuse your models, fix your schema and don‟t
hard-code your URLs

17. Handling Views (DOM)
• Usually your sequence is as simple as:
1.Update model  triggers change in views
2.Refresh views (render)  render template  apply into DOM
3.Notify the other views (if for some reason they cannot listen to the
same model)

18. Handling Views (DOM)
• Avoid spaghetti code
• Backbone expects to keep Models and Views in sync
• A view should only alter the parts of DOM it owns
• A view should not call directly other views than its children
• Use the event binding facilities offered by framework
(e.g. Backbone.view.events: {})
• A few jQuery calls to alter a subset of DOM is more code and more
expensive than replacing the same subset by a template
 Always drive your view changes through your model
 Use events for messaging between the application parts
 Use templates; usually it is ok to render the view again

19. Page Rendering – Templates
• Easier way of creating a bunch of HTML elements
• Inject HTML into DOM using $.html()
• The principle is the same in server-side: call template
with the parameters as data-object to get HTML
Samples: Handlebars, Dust.js, EJS, Google Closure
Templates
See: LinkedIn comparison of template engines

20. Summary
• SPA ~ MV(C) Pattern ~ Server API driven app
• A toolbelt of a JS framework and supplementary libraries
• Still fairly new paradigm, not in wide use yet
• Good complement to your existing web site
• Mobile/Hybrid app
• May replace your existing site when solving the crawling
issue

21. Further Reading
• HTML5 sovellusalustana (a book by Pyry L & Jukka K)
http://www.julkaisija.fi/yleista/html5.php
• Developing Backbone.js Applications (a CC book by Addy Osmani)
https://github.com/addyosmani/backbone-fundamentals
• HTML5 Rocks as a vault of information
http://www.html5rocks.com/en/
• A catalogue of JavaScript libraries to choose among
http://www.jsdb.io/

22. Thank you !
Lauri Svan
Software Architect, SC5 Online Ltd
https://github.com/laurisvan
https://twitter.com/laurisvan
HTML5 expertise at your service