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E B V N <title>Sample Page</title> in Font
E B V N <title>Sample Page</title> PDF-417 2d Barcode Generation In None Using Barcode printer for Font Control to generate, create PDF 417 image in Font applications. www.OnBarcode.comUPC-A Generator In None Using Barcode generator for Font Control to generate, create UPC-A Supplement 5 image in Font applications. www.OnBarcode.com</head> <script language="JavaScript" src="/lib/factory.js"></script> <script language="JavaScript" type="text/javascript"> var xmlhttp = FactoryXMLHttpRequest(); function GetIt(url) { if( xmlhttp) { xmlhttp.open('GET', url, false); xmlhttp.send(null); document.getElementById('result').innerHTML = xmlhttp.responseText; } } </script> </head> <body> <button onclick="GetIt('/cgross/books')">Get a document</button> <p><table border="1"> <tr><td>Document</td><td><span id="result">No Result</span></td></tr> </table></p> </body> </html> Print Code 3/9 In None Using Barcode printer for Font Control to generate, create ANSI/AIM Code 39 image in Font applications. www.OnBarcode.comEncoding EAN13 In None Using Barcode maker for Font Control to generate, create European Article Number 13 image in Font applications. www.OnBarcode.com<html><head>
PDF 417 Encoder In None Using Barcode generator for Font Control to generate, create PDF 417 image in Font applications. www.OnBarcode.comQR-Code Printer In None Using Barcode generator for Font Control to generate, create QR-Code image in Font applications. www.OnBarcode.comCHAPTER 2 THE NUTS AND BOLTS OF AJAX
Barcode Encoder In None Using Barcode maker for Font Control to generate, create Barcode image in Font applications. www.OnBarcode.comCodabar Printer In None Using Barcode drawer for Font Control to generate, create ANSI/AIM Codabar image in Font applications. www.OnBarcode.comThe rewritten page loads the XMLHttpRequest Factory pattern implementation by using a script tag, and assigning the attribute src to be the name of the file containing the Factory pattern implementation. Then, to instantiate and assign the XMLHttpRequest instance to the variable xmlhttp, the function FactoryXMLHttpRequest is called. The remaining code remains identical to the previous example because regardless of the browser, the methods of XMLHttpRequest are identical. Read PDF417 In VS .NET Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in .NET applications. www.OnBarcode.comRecognize PDF-417 2d Barcode In None Using Barcode reader for Software Control to read, scan read, scan image in Software applications. www.OnBarcode.comMaking Asynchronous Requests
Drawing PDF 417 In None Using Barcode encoder for Software Control to generate, create PDF-417 2d barcode image in Software applications. www.OnBarcode.comDenso QR Bar Code Recognizer In Visual Basic .NET Using Barcode scanner for .NET framework Control to read, scan read, scan image in .NET framework applications. www.OnBarcode.comThe Ajax examples used the XMLHttpRequest object in a synchronous manner, meaning that the moment send is called, the browser stops processing other messages and waits for an answer. To illustrate that a browser locks while processing synchronous requests, the previous Ajax application will retrieve a page from a server that will wait 10 seconds before returning the content. Following is the ASP.NET source code (note that this book will focus on both Java and ASP.NET): <%@ Page Language = "C#" %> <html> <head> <title>Hanging page</title> </head> <body> <% EBVN System.Threading.Thread.Sleep( 10000); %> Hello, after a ten second sleep! </body> </html> The ASP.NET sample is written by using the C# programming language. The single statement, System.Threading.Thread.Sleep, causes the current thread on the server to sleep for 10 seconds, which means that the browser will be waiting 10 seconds for its content to be retrieved. Modifying the previous Ajax application and clicking the button to retrieve the hanging page causes the browser to appear similar to Figure 2-5. In Figure 2-5, the clicked button remains pressed because it is waiting for the content to be returned. While the browser is waiting, the user cannot switch to another tab to process other HTTP requests. A hanging browser is a problem and will make the Ajax experience potentially painful for the user. Draw Data Matrix In None Using Barcode generator for Online Control to generate, create Data Matrix ECC200 image in Online applications. www.OnBarcode.comANSI/AIM Code 39 Creator In Java Using Barcode generation for Java Control to generate, create Code 39 Extended image in Java applications. www.OnBarcode.comCHAPTER 2 THE NUTS AND BOLTS OF AJAX
Make Barcode In Java Using Barcode generation for BIRT Control to generate, create Barcode image in BIRT applications. www.OnBarcode.comPDF-417 2d Barcode Creation In Java Using Barcode drawer for Java Control to generate, create PDF417 image in Java applications. www.OnBarcode.comFigure 2-5. Hanging browser waiting for content to be retrieved
Draw Code39 In Visual Basic .NET Using Barcode creation for .NET Control to generate, create Code 3 of 9 image in .NET applications. www.OnBarcode.comPrint Denso QR Bar Code In .NET Using Barcode generation for ASP.NET Control to generate, create QR-Code image in ASP.NET applications. www.OnBarcode.comEBVN
Encoding Barcode In None Using Barcode creator for Excel Control to generate, create Barcode image in Excel applications. www.OnBarcode.comEncoding Code 128 Code Set B In None Using Barcode encoder for Software Control to generate, create Code 128 Code Set A image in Software applications. www.OnBarcode.comThe solution is to use an asynchronous Ajax XMLHttpRequest request. An asynchronous request will not block the browser, and the user could continue clicking or using other tabs of the browser. The following source code rewrites the simple Ajax application to use an asynchronous request: <html> <head> <title>Sample Page</title> </head> <script language="JavaScript" src="/lib/factory.js"></script> <script language="JavaScript" type="text/javascript"> var xmlhttp = FactoryXMLHttpRequest(); function AsyncUpdateEvent() { switch(xmlhttp.readyState) { case 0: document.getElementById('status').innerHTML = "uninitialized"; break; case 1: document.getElementById('status').innerHTML = "loading"; break; case 2: document.getElementById('status').innerHTML = "loaded"; break; CHAPTER 2 THE NUTS AND BOLTS OF AJAX
case 3: document.getElementById('status').innerHTML = "interactive"; break; case 4: document.getElementById('status').innerHTML = "complete"; document.getElementById('result').innerHTML = xmlhttp.responseText; break; } } function GetIt(url) { if(xmlhttp) { xmlhttp.open('GET', url, true); xmlhttp.onreadystatechange = AsyncUpdateEvent; xmlhttp.send(null); } } </script> </head> <body> <button onclick="GetIt('/chap02/serverhang.aspx')">Get a document</button> <p><table border="1"> <tr> EBVN <td>Document</td> <td> <span id="status">No Result</span> </td> <td> <span id="result">No Result</span> </td></tr> </table></p> </body> </html> There are several new additions to the rewritten Ajax application, and they deal with the technical issues of loading content asynchronously. Let s start by focusing on the function GetIt. The implementation of GetIt is similar to previous Ajax application examples, except that the third parameter of the method open is true to indicate that the request will be asynchronous. This means that when the method send is called, the method will send the request, start another thread to wait for the response, and return immediately. Whenever XMLHttpRequest operates in asynchronous modes, feedback is given to the caller on the state of the request. The property onreadystatechange is a function that receives the feedback. It is important to note that the feedback function must be assigned before each send because upon completion of the request, the property onreadystatechange is reset. This is evident in the sources of the Mozilla-based browsers. The property onreadystatechange is assigned the function AsyncUpdateEvent. In the implementation of AsyncUpdateEvent is a switch statement that tests the current state of the request. When an asynchronous request is made, the script is free to continue executing other code.
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