A few slides to get people familiar with Windows 8 applications in JavaScript - WinJS, app lifecycle, app container, and more

1. Chad McCallum
ASP.NET/IIS MVP
iQmetrix Software
http://www.rtigger.com
@ChadEmm / chadm@iqmetrix.com

2. Windows RT API
 Windows Runtime is implemented at a low-level and
then “projected” into C++, C#, VB, and JavaScript APIs
 Allows the APIs to present the same functionality in a
way that’s familiar to developers of that language

3. Native App in HTML?
 Apps are run in an Internet Explorer 10 shell
 This means:
 Can include other JS libraries
 HTML5 and CSS3 support for user interface
 Can do (almost) anything you’d do with a web
application

4. What are these apps called?
 Windows Store apps
 Acquired, installed, and updated via the Windows Store
app
 Packaged into an “.appx” file when submitted
 Contains a manifest file that describes the app, the
resources it uses (camera, network, etc.), and lists OS
integrations (background tasks, file associations, etc.)

5. Windows Library for JavaScript
 aka WinJS
 Wrapper for Windows Runtime API
 Provides:
 Access to system-level resources
 HTML implementation of WinRT controls, complete
with CSS styling and events
 CSS3-based animation framework
 Helpers for common coding patterns

6. Not Quite a Web Page
 Some DOM API calls are modified or unavailable, like
alert or window.open
 There are some methods, properties, and CSS queries
that are specific to a Windows Store app
 Allowed to make cross-domain requests, load
resources from remote sources

7. Not Quite a Web Page
 Not allowed to reference scripts remotely
 IFrames are run in “web context” without access to
WinRT
 Some DOM-based calls are modified or removed
(document.write, innerHTML)

8. App Container
 Run within a dedicated environment that can’t access
other applications and the system directly
 Have unrestricted read/write access to their own
appdata folders
 Access to any other files or hardware goes through a
broker, which can deny access

9. App Lifecycle
 4-ish states
 Starting: shows splash screen image, does all the app
initialization behind the scenes
 Running: active application on user’s device
 Suspending: app has lost focus, 5 seconds to save state
 Resuming: app has regained focus
 Suspended: still in memory, but not allocated any CPU
time
 Terminated: removed from memory, effectively closed.
OS triggers this at will, app is not informed

10. App State
 When being “suspended”, Windows 8 gives your app
approximately 5 seconds to save its state
 Can save data as Temp, Local, and Roaming
 Save as a file and/or key-value pairs
 Always app-specific, as they’re saved relative to your
app’s directory
 Roaming settings are uploaded to user’s Microsoft
Account and are accessible across devices

11. Code Time!