Peter Lubbers - Pro HTML 5 Programming

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238 CHAPTER 9 ■ USING THE HTML5 WEB STORAGE API } }); }); function initDatabase() { var names = ["Peter Lubbers", "Brian Albers", "Frank Salim"]; db.transaction(function (tx) { tx.executeSql('CREATE TABLE IF NOT EXISTS racers (id integer primary key� autoincrement, name)'); } initDatabase(); for (var i=0; i
Listing 9-14. JSON Object Storage var data; function loadData() { data = JSON.parse(sessionStorage["myStorageKey"]) } function saveData() { sessionStorage["myStorageKey"] = JSON.stringify(data); } window.addEventListener("load", loadData, true); window.addEventListener("unload", saveData, true); CHAPTER 9 ■ USING THE HTML5 WEB STORAGE API As you can see, the script contains event listeners to register handlers for load and unload events in the browser window. In this case, the handlers call the loadData() and saveData() functions, respectively. In the loadData() function, the session storage area is queried for the value of a storage key, and that key is passed to the JSON.parse() function. The JSON.parse() routine will take a previously saved string representation of an object and reconstitute it into a copy of the original. This routine is called every time the page loads. Similarly, the saveData() function takes a data value and calls JSON.stringify() on it to turn it into a string representation of the object. That string is, in turn, stored back into storage. By registering the saveData() function on the unload browser event, we ensure that it is called every time the user navigates away or shuts down the browser or window. The practical result of these two functions is that any object we wish to track in storage, no matter if it is a complex object type, can be stored and reloaded as users navigate in and out of the application. This allows developers to extend the techniques we have already shown to nontext data. A Window into Sharing As alluded to in an earlier section, the ability for HTML5 Web Storage events to fire in any window browsing the same origin has some powerful implications. It means that storage can be used to send messages from window to window, even if they are not all using the storage object itself. This, in turn implies that we can now share data across windows that have the same origin. Let’s see how this works using some code samples. To listen to cross-window messages, a simple script needs only to register a handler for storage events. Let’s assume that a page running at http://www.example.com/storageLog.html contains the code shown in Listing 9-15 (the sample file storageLog.html for this example is also located in the code/storage folder): 239
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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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Peter Lubbers - Pro HTML 5 Programming

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