Peter Lubbers - Pro HTML 5 Programming

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Download from Wow! eBook 222 CHAPTER 9 ■ USING THE HTML5 WEB STORAGE API As you can see, the name storage is used to indicate interest in storage events. Any time a Storage event—either sessionStorage or localStorage—for that origin is raised any registered event listener will receive the storage event as the specified event handler. The storage event itself takes the form shown in Listing 9-3. Listing 9-3. The StorageEvent Interface interface StorageEvent : Event { readonly attribute DOMString key; readonly attribute any oldValue; readonly attribute any newValue; readonly attribute DOMString url; readonly attribute Storage storageArea; }; The StorageEvent object will be the first object passed to the event handler, and it contains all the information necessary to understand the nature of the storage change. • The key attribute contains the key value that was updated or removed in the storage. • The oldValue contains the previous value corresponding to the key before it was updated, and the newValue contains the value after the change. If the value was newly added, the oldValue will be null, and if the value has been removed, the newValue will be null. • The url will point to the origin where the storage event occurred. • Finally, the storageArea provides a convenient reference to the sessionStorage or localStorage where the value was changed. This gives the handler an easy way to query the storage for current values or make changes based on other storage changes. Listing 9-4 shows a simple event handler, which will raise an alert dialog with the contents of any storage event fired on the page’s origin. Listing 9-4. Event Handler that Displays Content of a Storage Event // display the contents of a storage event function displayStorageEvent(e) { var logged = "key:" + e.key + ", newValue:" + e.newValue + ", oldValue:" + e.oldValue +", url:" + e.url + ", storageArea:" + e.storageArea; alert(logged); } // add a storage event listener for this origin window.addEventListener("storage", displayStorageEvent, true);
Exploring Web Storage CHAPTER 9 ■ USING THE HTML5 WEB STORAGE API Since HTML5 Web Storage is very similar in function to cookies, it is not too surprising that the most advanced browsers are treating them in a very similar manner. Values that are stored into localStorage or sessionStorage can be browsed similar to cookies in the latest browsers, as shown in Figure 9-4. Figure 9-4. Storage values in Google Chrome’s Storage Panel This interface also grants users the ability to remove storage values as desired and easily see what values a given web site is recording while they visit the pages. Not surprisingly, the Safari browser from Apple has a similar, unified display for cookies and storage, as it is based on the same underlying WebKit rendering engine as Chrome is. Figure 9-5 shows the Safari Storage panel. Figure 9-5. Storage values in Safari’s Storage panel The Opera browsers goes one step further, by allowing users to not only browse and delete storage values but also create them as shown in Figure 9-6. 223
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THE EXPERT’S VOICE ® IN WEB DEVE
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■ ■ ■ Pro HTML5 Programming P
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For my beautiful wife, Vittoria, an
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Contents ■Foreword ..............
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■ CONTENTS Implementing Canvas Se
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■ CONTENTS Summary ..............
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■ CONTENTS Setting and Retrieving
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Foreword In June 2004, representati
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About the Technical Reviewer � Pa
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Introduction HTML5 is brand new. In
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C H A P T E R 1 ■ ■ ■ Overvie
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CHAPTER 1 ■ OVERVIEW OF HTML5 wit
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Interoperability Simplification CHA
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• MathML • Microdata • Server
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Figure 1-1. A page rendered in stan
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Table 1-2. New sectioning HTML5 ele
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CHAPTER 1 ■ OVERVIEW OF HTML5 Wit
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article { background-color: #eee; d
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Figure 1-2. An HTML5 page with all
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CHAPTER 1 ■ OVERVIEW OF HTML5 The
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Figure 1-3. Developer Tools view in
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CHAPTER 1 ■ OVERVIEW OF HTML5 All
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26 CHAPTER 2 ■ USING THE HTML5 CA
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C H A P T E R 3 ■ ■ ■ Working
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Audio and Video Codecs CHAPTER 3
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Table 3-1. Browser support for HTML
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MEDIA FOR EVERYONE CHAPTER 3 ■ WO
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CHAPTER 3 ■ WORKING WITH HTML5 AU
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Table 3-4 shows a few of the read-o
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find the actual frame since the vid
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LOSING VIEWERS IN THE OF AN EYE CH
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C H A P T E R 4 ■ ■ ■ Using t
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A device can use any of the followi
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Table 4-4. Pros and cons of cell ph
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Figure 4-1. HTML5 Geolocation brows
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CHAPTER 4 ■ USING THE HTML5 GEOLO
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Listing 4-6. The Haversine formula
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Listing 4-9. Adding the loadDemo()
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THE EASIEST WAY TO TRAVEL CHAPTER 4
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var deltaLatitude = toRadians(latit
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Practical Extras CHAPTER 4 ■ USIN
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Show Me on a Google Map CHAPTER 4
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CHAPTER 5 ■ USING THE COMMUNICATI
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var defaultTitle = "Portal [http://
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Send Notification CHAPTER 5 ■ U
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Figure 5-4. Difference between clie
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“SEEMINGLY ARBITRARY” TIMES CHA
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crossOriginRequest.upload.onprogres
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Figure 6-1. The complexity of real-
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Listing 6-2. The WebSocket interfac
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Listing 6-4. HTTP response header H
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Figure 6-4. Latency comparison betw
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EXISTING WEBSOCKET SERVERS CHAPTER
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CHAPTER 6 ■ USING THE HTML5 WEBSO
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def terminate(self): self.ready_sta
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self.sessions = [] self.port = port
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Basic API Usage CHAPTER 6 ■ USING
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HTML5 WebSocket / Geolocation Track
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} } Summary incomingRow = docume
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170 CHAPTER 7 ■ USING THE HTML5 F
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274 ■ INDEX Web SQL database supp
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276 ■ INDEX HTML5 page CSS file f
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278 ■ INDEX media elements. See a
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280 ■ INDEX building application
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284 ■ INDEX stopping Web Workers,
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Peter Lubbers - Pro HTML 5 Programming

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