Peter Lubbers - Pro HTML 5 Programming

Recommendations

Info

154 CHAPTER 6 ■ USING THE HTML5 WEBSOCKET API Using the HTML5 WebSocket API In this section, we’ll explore the use of HTML5 WebSocket in more detail. Checking for Browser Support Before you use the HTML5 WebSocket API, you will want to make sure there is support in the browser for what you’re about to do. This way, you can provide some alternate text, prompting the users of your application to upgrade to a more up-to-date browser. Listing 6-9 shows one way you can test for browser support. Listing 6-7. Checking for browser support function loadDemo() { if (window.WebSocket) { document.getElementById("support").innerHTML = "HTML5 WebSocket is supported in your browser."; } else { document.getElementById("support").innerHTML = "HTML5 WebSocket is not supported in your browser."; } } In this example, you test for browser support in the loadDemo function, which might be called when the application’s page is loaded. A call to window.WebSocket will return the WebSocket object if it exists, or trigger the failure case if it does not. In this case, the page is updated to reflect whether there is browser support or not by updating a previously defined support element on the page with a suitable message. Another way to see if HTML5 WebSocket is supported in your browser, is to use the browser’s console (Firebug or Chrome Developer Tools for example). Figure 6-5 shows how you can test whether WebSockets is supported natively in Google Chrome (if it is not, the window.WebSocket command returns “undefined.”) Figure 6-5. Testing WebSocket support in Google Chrome Developer Tools
Basic API Usage CHAPTER 6 ■ USING THE HTML5 WEBSOCKET API The sample code for the following examples is located on the book web site in the WebSockets section. This folder contains a websocket.html file and a broadcast.html file (and a tracker.html file used in the following section) as well as the WebSocket server code shown previously that can be run in Python. Creating a WebSocket object and Connecting to a WebSocket Server Using the WebSocket interface is straight-forward. To connect to an end-point, just create a new WebSocket instance, providing the new object with a URL that represents the end-point to which you wish to connect. You can use the ws:// and wss:// prefixes are to indicate a WebSocket and a WebSocket Secure connection, respectively. url = "ws://localhost:8080/echo"; w = new WebSocket(url); Adding Event Listeners WebSocket programming follows an asynchronous programming model; once you have an open socket, you simply wait for events. You don’t have to actively poll the server anymore. To do this, you add callback functions to the WebSocket object to listen for events. A WebSocket object dispatches three events: open, close, and message. The open event fires when a connection is established, the message event fires when messages are received, and the close event fires when the WebSocket connection is closed. As in most JavaScript APIs, there are corresponding callbacks (onopen, onmessage, and onclose) that are called when the events are dispatched. w.onopen = function() { log("open"); w.send("thank you for accepting this websocket request"); } w.onmessage = function(e) { log(e.data); } w.onclose = function(e) { log("closed"); } Sending Messages While the socket is open (that is, after the onopen listener is called and before the onclose listener is called), you can use the send method to send messages. After sending the message, you can also call close to terminate the connection, but you can also leave the connection open. document.getElementById("sendButton").onclick = function() { w.send(document.getElementById("inputMessage").value); } 155
Page 1 and 2:
THE EXPERT’S VOICE ® IN WEB DEVE
Page 3 and 4:
■ ■ ■ Pro HTML5 Programming P
Page 5 and 6:
For my beautiful wife, Vittoria, an
Page 7 and 8:
Contents ■Foreword ..............
Page 9 and 10:
■ CONTENTS Implementing Canvas Se
Page 11 and 12:
■ CONTENTS Summary ..............
Page 13 and 14:
■ CONTENTS Setting and Retrieving
Page 15 and 16:
Foreword In June 2004, representati
Page 17 and 18:
About the Technical Reviewer � Pa
Page 19 and 20:
Introduction HTML5 is brand new. In
Page 21 and 22:
C H A P T E R 1 ■ ■ ■ Overvie
Page 23 and 24:
CHAPTER 1 ■ OVERVIEW OF HTML5 wit
Page 25 and 26:
Interoperability Simplification CHA
Page 27 and 28:
• MathML • Microdata • Server
Page 29 and 30:
Figure 1-1. A page rendered in stan
Page 31 and 32:
Table 1-2. New sectioning HTML5 ele
Page 33 and 34:
CHAPTER 1 ■ OVERVIEW OF HTML5 Wit
Page 35 and 36:
article { background-color: #eee; d
Page 37 and 38:
Figure 1-2. An HTML5 page with all
Page 39 and 40:
CHAPTER 1 ■ OVERVIEW OF HTML5 The
Page 41 and 42:
Figure 1-3. Developer Tools view in
Page 43:
CHAPTER 1 ■ OVERVIEW OF HTML5 All
Page 46 and 47:
26 CHAPTER 2 ■ USING THE HTML5 CA
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Download from Wow! eBook 32 CHAPTE
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 85 and 86:
C H A P T E R 3 ■ ■ ■ Working
Page 87 and 88:
Audio and Video Codecs CHAPTER 3
Page 89 and 90:
Table 3-1. Browser support for HTML
Page 91 and 92:
MEDIA FOR EVERYONE CHAPTER 3 ■ WO
Page 93 and 94:
CHAPTER 3 ■ WORKING WITH HTML5 AU
Page 95 and 96:
Table 3-4 shows a few of the read-o
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
find the actual frame since the vid
Page 105 and 106:
LOSING VIEWERS IN THE OF AN EYE CH
Page 107 and 108:
C H A P T E R 4 ■ ■ ■ Using t
Page 109 and 110:
A device can use any of the followi
Page 111 and 112:
Table 4-4. Pros and cons of cell ph
Page 113 and 114:
Figure 4-1. HTML5 Geolocation brows
Page 115 and 116:
CHAPTER 4 ■ USING THE HTML5 GEOLO
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124: Listing 4-6. The Haversine formula
Page 125 and 126: Listing 4-9. Adding the loadDemo()
Page 127 and 128: THE EASIEST WAY TO TRAVEL CHAPTER 4
Page 129 and 130: var deltaLatitude = toRadians(latit
Page 131 and 132: Practical Extras CHAPTER 4 ■ USIN
Page 133 and 134: Show Me on a Google Map CHAPTER 4
Page 135 and 136: C H A P T E R 5 ■ ■ ■ Using t
Page 137 and 138: CHAPTER 5 ■ USING THE COMMUNICATI
Page 143 and 144: var defaultTitle = "Portal [http://
Page 145 and 146: Send Notification CHAPTER 5 ■ U
Page 147 and 148: Figure 5-4. Difference between clie
Page 149 and 150: “SEEMINGLY ARBITRARY” TIMES CHA
Page 151 and 152: crossOriginRequest.upload.onprogres
Page 157 and 158: C H A P T E R 6 ■ ■ ■ Using t
Page 159 and 160: Figure 6-1. The complexity of real-
Page 161 and 162: Listing 6-2. The WebSocket interfac
Page 163 and 164: Listing 6-4. HTTP response header H
Page 165 and 166: Figure 6-4. Latency comparison betw
Page 167 and 168: EXISTING WEBSOCKET SERVERS CHAPTER
Page 169 and 170: CHAPTER 6 ■ USING THE HTML5 WEBSO
Page 171 and 172: def terminate(self): self.ready_sta
Page 173: self.sessions = [] self.port = port
Page 185 and 186: HTML5 WebSocket / Geolocation Track
Page 187: } } Summary incomingRow = docume
Page 190 and 191: 170 CHAPTER 7 ■ USING THE HTML5 F
Page 192 and 193: Download from Wow! eBook 172 CHAPT
Page 212 and 213: Download from Wow! eBook
Page 214 and 215: 194 CHAPTER 8 ■ USING THE HTML5 W
Page 224 and 225:
204 CHAPTER 8 ■ USING THE HTML5 W
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Download from Wow! eBook 212 CHAPT
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Page 254 and 255:
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
Download from Wow! eBook
Page 264 and 265:
244 CHAPTER 10 ■ CREATING HTML5 O
Page 266 and 267:
Page 268 and 269:
Page 270 and 271:
Page 272 and 273:
Page 274 and 275:
Page 276 and 277:
Page 279 and 280:
C H A P T E R 11 ■ ■ ■ The Fu
Page 281 and 282:
Figure 11-1. Quake II 3D Shaders CH
Page 283 and 284:
CHAPTER 11 ■ THE FUTURE OF HTML5
Page 285 and 286:
Page 287:
Page 290 and 291:
270 ■ INDEX unsupported, 68 using
Page 292 and 293:
Download from Wow! eBook 272 ■ I
Page 294 and 295:
274 ■ INDEX Web SQL database supp
Page 296 and 297:
276 ■ INDEX HTML5 page CSS file f
Page 298 and 299:
278 ■ INDEX media elements. See a
Page 300 and 301:
280 ■ INDEX building application
Page 302 and 303:
Download from Wow! eBook 282 ■ I
Page 304:
284 ■ INDEX stopping Web Workers,
show all

Peter Lubbers - Pro HTML 5 Programming

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?