Peter Lubbers - Pro HTML 5 Programming

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134 CHAPTER 5 ■ USING THE COMMUNICATION APIS XMLHttpRequest Level 2 Geolocation Data to upload: Upload geoData = [[39.080018000000003, 39.112557000000002, 39.135261, 39.150458, 39.170653000000001, 39.190128000000001, 39.204510999999997, 39.226759000000001, 39.238483000000002, 39.228154000000004, 39.249400000000001, 39.249533, 39.225276999999998, 39.191253000000003, 39.167993000000003, 39.145685999999998, 39.121620999999998, 39.095761000000003, 39.080593, 39.053131999999998, 39.02619, 39.002929000000002, 38.982886000000001, 38.954034999999998, 38.944926000000002, 38.919960000000003, 38.925261999999996, 38.934922999999998, 38.949373000000001, 38.950133999999998, 38.952649000000001, 38.969692000000002, 38.988512999999998, 39.010652, 39.033088999999997, 39.053493000000003, 39.072752999999999], [-120.15724399999999, -120.15818299999999, - 120.15600400000001, -120.14564599999999, -120.141285, -120.10889900000001, - 120.09528500000002, -120.077596, -120.045428, -120.0119, -119.98897100000002, - 119.95124099999998, -119.93270099999998, -119.927131, -119.92685999999999, - 119.92636200000001, -119.92844600000001, -119.911036, -119.942834, -119.94413000000002, - 119.94555200000001, -119.95411000000001, -119.941327, -119.94605900000001, - 119.97527599999999, -119.99445, -120.028998, -120.066335, -120.07867300000001, -120.089985, -120.112227, -120.09790700000001, -120.10881000000001, -120.116692, -120.117847, - 120.11727899999998, -120.14398199999999]]; Status: ready The Application in Action To see this example in action, there are two prerequisites: the pages have to be served up from different domains, and the target page has to be served up by a web server that understands CORS headers. A CORS-compliant Python script that can handle incoming cross-origin XMLHttpRequests is included in the example code for this chapter. You can run the demo on your local machine by performing the following steps: 1. Update your hosts file (C:\Windows\system32\drivers\etc\hosts on Windows or /etc/hosts on Unix/Linux) by adding two entries pointing to your localhost (IP address 127.0.0.1) as shown in the following example: 127.0.0.1 geodata.example.net 127.0.0.1 portal.example.com
CHAPTER 5 ■ USING THE COMMUNICATION APIS ■ Note You must restart your browser after modifying the host file to ensure the DNS entries take effect. 2. Install Python, which includes the lightweight SimpleHTTPServer web server, if you did not do so for the previous example. 3. Navigate to the directory that contains the example file (crossOrignUpload.html) and the Python CORS server script (CORSServer.py). 4. Start Python in this directory as follows: python CORSServer.py 9999 5. Open a browser and navigate to http://portal.example.com:9999/crossOriginUpload.html. You should now see the page shown in Figure 5.5. Practical Extras Sometimes there are techniques that don’t fit into our regular examples, but that nonetheless apply to many types of <strong>HTML</strong>5 applications. We present to you some short, but common, practical extras here. Structured Data Early versions of postMessage only supported strings. Later revisions allowed other types of data including JavaScript objects, canvas imageData, and files. Support for different object types will vary by browser as the specification develops. In some browsers, the limitations on JavaScript objects that can be sent with postMessage are the same as those for JSON data. In particular, data structures with cycles may not be allowed. An example of this is a list containing itself. Framebusting Framebusting is a technique for ensuring that your content is not loaded in an iframe. An application can detect that its window is not the outermost window (window.top) and subsequently break out of its containing frame, as shown in the following example. if (window !== window.top) { window.top.location = location; } However, there may be certain partner pages that you want to allow to frame your content. One solution is to use postMessage to handshake between cooperating iframes and containing pages, as shown in the Listing 5-11. 135
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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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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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C H A P T E R 11 ■ ■ ■ The Fu
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CHAPTER 11 ■ THE FUTURE OF HTML5
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Peter Lubbers - Pro HTML 5 Programming

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