- •Contents at a Glance
- •Contents
- •Foreword
- •About the Authors
- •About the Technical Reviewer
- •Acknowledgments
- •Introduction
- •Who This Book Is For
- •An Overview of This Book
- •Example Code and Companion Web Site
- •Contacting the Authors
- •Overview of HTML5
- •The Story So Far—The History of HTML5
- •The Myth of 2022 and Why It Doesn’t Matter
- •Who Is Developing HTML5?
- •A New Vision
- •Compatibility and Paving the Cow Paths
- •Utility and the Priority of Constituencies
- •Interoperability Simplification
- •Universal Access
- •A Plugin–Free Paradigm
- •What’s In and What’s Out?
- •What’s New in HTML5?
- •New DOCTYPE and Character Set
- •New and Deprecated Elements
- •Semantic Markup
- •Simplifying Selection Using the Selectors API
- •JavaScript Logging and Debugging
- •window.JSON
- •DOM Level 3
- •Monkeys, Squirrelfish, and Other Speedy Oddities
- •Summary
- •Using the Canvas API
- •Overview of HTML5 Canvas
- •History
- •What Is a Canvas?
- •Canvas Coordinates
- •When Not to Use Canvas
- •Fallback Content
- •CSS and Canvas
- •Browser Support for HTML5 Canvas
- •Using the HTML5 Canvas APIs
- •Checking for Browser Support
- •Adding a Canvas to a Page
- •Applying Transformations to Drawings
- •Working with Paths
- •Working with Stroke Styles
- •Working with Fill Styles
- •Filling Rectangular Content
- •Drawing Curves
- •Inserting Images into a Canvas
- •Using Gradients
- •Using Background Patterns
- •Scaling Canvas Objects
- •Using Canvas Transforms
- •Using Canvas Text
- •Applying Shadows
- •Working with Pixel Data
- •Implementing Canvas Security
- •Building an Application with HTML5 Canvas
- •Practical Extra: Full Page Glass Pane
- •Practical Extra: Timing Your Canvas Animation
- •Summary
- •Working with Scalable Vector Graphics
- •Overview of SVG
- •History
- •Understanding SVG
- •Scalable Graphics
- •Creating 2D Graphics with SVG
- •Adding SVG to a Page
- •Simple Shapes
- •Transforming SVG Elements
- •Reusing Content
- •Patterns and Gradients
- •SVG Paths
- •Using SVG Text
- •Putting the Scene Together
- •Building an Interactive Application with SVG
- •Adding Trees
- •Adding the updateTrees Function
- •Adding the removeTree Function
- •Adding the CSS Styles
- •The Final Code
- •Summary
- •Working with Audio and Video
- •Overview of Audio and Video
- •Video Containers
- •Audio and Video Codecs
- •Audio and Video Restrictions
- •Browser Support for Audio and Video
- •Using the Audio and Video API
- •Checking for Browser Support
- •Accessibility
- •Understanding Media Elements
- •Working with Audio
- •Working with Video
- •Practical Extras
- •Summary
- •Using the Geolocation API
- •About Location Information
- •Latitude and Longitude Coordinates
- •Where Does Location Information Come From?
- •IP Address Geolocation Data
- •GPS Geolocation Data
- •Wi-Fi Geolocation Data
- •Cell Phone Geolocation Data
- •User–Defined Geolocation Data
- •Browser Support for Geolocation
- •Privacy
- •Triggering the Privacy Protection Mechanism
- •Dealing with Location Information
- •Using the Geolocation API
- •Checking for Browser Support
- •Position Requests
- •Building an Application with Geolocation
- •Writing the HTML Display
- •Processing the Geolocation Data
- •The Final Code
- •Practical Extras
- •What’s My Status?
- •Show Me on a Google Map
- •Summary
- •Using the Communication APIs
- •Cross Document Messaging
- •Understanding Origin Security
- •Browser Support for Cross Document Messaging
- •Using the postMessage API
- •Building an Application Using the postMessage API
- •XMLHttpRequest Level 2
- •Cross-Origin XMLHttpRequest
- •Progress Events
- •Browser Support for HTML5 XMLHttpRequest Level 2
- •Using the XMLHttpRequest API
- •Building an Application Using XMLHttpRequest
- •Practical Extras
- •Structured Data
- •Framebusting
- •Summary
- •Using the WebSocket API
- •Overview of WebSocket
- •Real-Time and HTTP
- •Understanding WebSocket
- •Writing a Simple Echo WebSocket Server
- •Using the WebSocket API
- •Checking for Browser Support
- •Basic API Usage
- •Building a WebSocket Application
- •Coding the HTML File
- •Adding the WebSocket Code
- •Adding the Geolocation Code
- •Putting It All Together
- •The Final Code
- •Summary
- •Using the Forms API
- •Overview of HTML5 Forms
- •HTML Forms Versus XForms
- •Functional Forms
- •Browser Support for HTML5 Forms
- •An Input Catalog
- •Using the HTML5 Forms APIs
- •New Form Attributes and Functions
- •Checking Forms with Validation
- •Validation Feedback
- •Building an Application with HTML5 Forms
- •Practical Extras
- •Summary
- •Working with Drag-and-Drop
- •Web Drag-and-Drop: The Story So Far
- •Overview of HTML5 Drag-and-Drop
- •The Big Picture
- •Events to Remember
- •Drag Participation
- •Transfer and Control
- •Building an Application with Drag-and-Drop
- •Getting Into the dropzone
- •Handling Drag-and-Drop for Files
- •Practical Extras
- •Customizing the Drag Display
- •Summary
- •Using the Web Workers API
- •Browser Support for Web Workers
- •Using the Web Workers API
- •Checking for Browser Support
- •Creating Web Workers
- •Loading and Executing Additional JavaScript
- •Communicating with Web Workers
- •Coding the Main Page
- •Handling Errors
- •Stopping Web Workers
- •Using Web Workers within Web Workers
- •Using Timers
- •Example Code
- •Building an Application with Web Workers
- •Coding the blur.js Helper Script
- •Coding the blur.html Application Page
- •Coding the blurWorker.js Web Worker Script
- •Communicating with the Web Workers
- •The Application in Action
- •Example Code
- •Summary
- •Using the Storage APIs
- •Overview of Web Storage
- •Browser Support for Web Storage
- •Using the Web Storage API
- •Checking for Browser Support
- •Setting and Retrieving Values
- •Plugging Data Leaks
- •Local Versus Session Storage
- •Other Web Storage API Attributes and Functions
- •Communicating Web Storage Updates
- •Exploring Web Storage
- •Building an Application with Web Storage
- •The Future of Browser Database Storage
- •The Web SQL Database
- •The Indexed Database API
- •Practical Extras
- •JSON Object Storage
- •A Window into Sharing
- •Summary
- •Overview of HTML5 Offline Web Applications
- •Browser Support for HTML5 Offline Web Applications
- •Using the HTML5 Application Cache API
- •Checking for Browser Support
- •Creating a Simple Offline Application
- •Going Offline
- •Manifest Files
- •The ApplicationCache API
- •Application Cache in Action
- •Building an Application with HTML5 Offline Web Applications
- •Creating a Manifest File for the Application Resources
- •Creating the HTML Structure and CSS for the UI
- •Creating the Offline JavaScript
- •Check for ApplicationCache Support
- •Adding the Update Button Handler
- •Add Geolocation Tracking Code
- •Adding Storage Code
- •Adding Offline Event Handling
- •Summary
- •The Future of HTML5
- •Browser Support for HTML5
- •HTML Evolves
- •WebGL
- •Devices
- •Audio Data API
- •Touchscreen Device Events
- •Peer-to-Peer Networking
- •Ultimate Direction
- •Summary
- •Index
CHAPTER 12 ■ CREATING OFFLINE WEB APPLICATIONS
<link rel="stylesheet" href="html5.css"> </head>
<body>
<header>
<h1>Offline Example</h1> </header>
<section>
<article>
<button id="installButton">Check for Updates</button> <h3>Log</h3>
<div id="info"> </div>
</article>
</section>
</body>
</html>
There are a couple of things to note in this HTML that pertain to this application's offline capabilities. The first is the manifest attribute on the HTML element. Most of the HTML examples in this book omit the <html> element because it is optional in HTML5. However, the ability to cache offline depends on specifying the manifest file there.
The second thing to note is the button. That will give the user control over configuring this application for offline use.
Creating the Offline JavaScript
For this example, the JavaScript is contained in multiple .js files included with <script> tags. These scripts are cached along with the HTML and CSS.
<offline.js>
/*
* log each of the events fired by window.applicationCache */
window.applicationCache.onchecking = function(e) { log("Checking for application update");
}
window.applicationCache.onnoupdate = function(e) { log("No application update found");
}
window.applicationCache.onupdateready = function(e) { log("Application update ready");
}
window.applicationCache.onobsolete = function(e) { log("Application obsolete");
}
window.applicationCache.ondownloading = function(e) {
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CHAPTER 12 ■ CREATING OFFLINE WEB APPLICATIONS
log("Downloading application update");
}
window.applicationCache.oncached = function(e) { log("Application cached");
}
window.applicationCache.onerror = function(e) { log("Application cache error");
}
window.addEventListener("online", function(e) { log("Online");
}, true);
window.addEventListener("offline", function(e) { log("Offline");
}, true);
/*
* Convert applicationCache status codes into messages */
showCacheStatus = function(n) {
statusMessages = ["Uncached","Idle","Checking","Downloading","Update Ready","Obsolete"]; return statusMessages[n];
}
install = function() { log("Checking for updates"); try {
window.applicationCache.update(); } catch (e) {
applicationCache.onerror();
}
}
onload = function(e) {
// Check for required browser features if (!window.applicationCache) {
log("HTML5 Offline Applications are not supported in your browser."); return;
}
if (!navigator.geolocation) {
log("HTML5 Geolocation is not supported in your browser."); return;
}
if (!window.localStorage) {
log("HTML5 Local Storage not supported in your browser."); return;
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CHAPTER 12 ■ CREATING OFFLINE WEB APPLICATIONS
}
log("Initial cache status: " + showCacheStatus(window.applicationCache.status)); document.getElementById("installButton").onclick = checkFor;
}
<log.js>
log = function() {
var p = document.createElement("p");
var message = Array.prototype.join.call(arguments, " "); p.innerHTML = message; document.getElementById("info").appendChild(p);
}
Check for ApplicationCache Support
In addition to the offline application cache, this example uses geolocation and local storage. We ensure that the browser supports all of these features when the page loads.
onload = function(e) {
// Check for required browser features if (!window.applicationCache) {
log("HTML5 Offline Applications are not supported in your browser."); return;
}
if (!navigator.geolocation) {
log("HTML5 Geolocation is not supported in your browser."); return;
}
if (!window.localStorage) {
log("HTML5 Local Storage is not supported in your browser."); return;
}
if (!window.WebSocket) {
log("HTML5 WebSocket is not supported in your browser."); return;
}
log("Initial cache status: " + showCacheStatus(window.applicationCache.status)); document.getElementById("installButton").onclick = install;
}
Adding the Update Button Handler
Next, add an update handler that updates the application cache as follows:
install = function() { log("Checking for updates"); try {
window.applicationCache.update();
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CHAPTER 12 ■ CREATING OFFLINE WEB APPLICATIONS
} catch (e) { applicationCache.onerror();
}
}
Clicking this button will explicitly start the cache check that will cause all cache resources to be downloaded if necessary. When available updates have completely downloaded, a message is logged in the UI. At this point, the user knows that the application has successfully installed and can be run in offline mode.
Add Geolocation Tracking Code
This code is based on the geolocation code from Chapter 4. It is contained in the tracker.js JavaScript file.
/*
* Track and report the current location */
var handlePositionUpdate = function(e) { var latitude = e.coords.latitude; var longitude = e.coords.longitude;
log("Position update:", latitude, longitude); if(navigator.onLine) {
uploadLocations(latitude, longitude);
}
storeLocation(latitude, longitude);
}
var handlePositionError = function(e) { log("Position error");
}
var uploadLocations = function(latitude, longitude) { var request = new XMLHttpRequest();
request.open("POST", "http://geodata.example.net:8000/geoupload", true); request.send(localStorage.locations);
}
var geolocationConfig = {"maximumAge":20000};
navigator.geolocation.watchPosition(handlePositionUpdate,
handlePositionError,
geolocationConfig);
Adding Storage Code
Next, add the code that writes updates to localStorage when the application is in offline mode.
var storeLocation = function(latitude, longitude) { // load stored location list
var locations = JSON.parse(localStorage.locations || "[]"); // add location
310