AJAX and PHP

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AJAX and the Future of Web Applications cross-browser compatible—we'll discuss the details in Chapter 2, for now it's important to know what it does. The XMLHttpRequest instance, called xmlHttp, is used in process() to make the asynchronous server request: // make asynchronous HTTP request using the XMLHttpRequest object function process() { // proceed only if the xmlHttp object isn't busy if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0) { // retrieve the name typed by the user on the form name = encodeURIComponent(document.getElementById("myName").value); // execute the quickstart.php page from the server xmlHttp.open("GET", "quickstart.php?name=" + name, true); // define the method to handle server responses xmlHttp.onreadystatechange = handleServerResponse; // make the server request xmlHttp.send(null); } else // if the connection is busy, try again after one second setTimeout('process()', 1000); } What you see here is, actually, the heart of AJAX—the code that makes the asynchronous call to the server. Why is it so important to call the server asynchronously? Asynchronous requests, by their nature, don't freeze processing (and user experience) while the call is made, until the response is received. Asynchronous processing is implemented by event-driven architectures, a good example being the way graphical user interface code is built: without events, you'd probably need to check continuously if the user has clicked a button or resized a window. Using events, the button notifies the application automatically when it has been clicked, and you can take the necessary actions in the event handler function. With AJAX, this theory applies when making a server request—you are automatically notified when the response comes back. If you're curious to see how the application would work using a synchronous request, you need to change the third parameter of xmlHttp.open to false, and then call handleServerResponse manually, as shown below. If you try this, the input box where you're supposed to write your name will freeze when the server is contacted (in this case the freeze length depends largely on the connection speed, so it may not be very noticeable if you're running the server on the local machine). // function calls the server using the XMLHttpRequest object function process() { // retrieve the name typed by the user on the form name = encodeURIComponent(document.getElementById("myName").value); // execute the quickstart.php page from the server xmlHttp.open("GET", "quickstart.php?name=" + name, false); // make synchronous server request (freezes processing until completed) xmlHttp.send(null); // read the response handleServerResponse(); } The process() function is supposed to initiate a new server request using the XMLHttpRequest object. However, this is only possible if the XMLHttpRequest object isn't busy making another 26 www.it-ebooks.info
Chapter 1 request. In our case, this can happen if it takes more than one second for the server to reply, which could happen if the Internet connection is very slow. So, process() starts by verifying that it is clear to initiate a new request: // make asynchronous HTTP request using the XMLHttpRequest object function process() { // proceed only if the xmlHttp object isn't busy if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0) { So, if the connection is busy, we use setTimeout to retry after one second (the function's second argument specifies the number of milliseconds to wait before executing the piece of code specified by the first argument: // if the connection is busy, try again after one second setTimeout('process()', 1000); If the line is clear, you can safely make a new request. The line of code that prepares the server request but doesn't commit it is: // execute the quickstart.php page from the server xmlHttp.open("GET", 'quickstart.php?name=' + name, true); The first parameter specifies the method used to send the user name to the server, and you can choose between GET and POST (learn more about them in Chapter 3). The second parameter is the server page you want to access; when the first parameter is GET, you send the parameters as name/value pairs in the query string. The third parameter is true if you want the call to be made asynchronously. When making asynchronous calls, you don't wait for a response. Instead, you define another function to be called automatically when the state of the request changes: // define the method to handle server responses xmlHttp.onreadystatechange = handleServerResponse; Once you've set this option, you can rest calm—the handleServerResponse function will be executed by the system when anything happens to your request. After everything is set up, you initiate the request by calling XMLHttpRequest's send method: } // make the server request xmlHttp.send(null); Let's now look at the handleServerResponse function: // executed automatically when a message is received from the server function handleServerResponse() { // move forward only if the transaction has completed if (xmlHttp.readyState == 4) { // status of 200 indicates the transaction completed successfully if (xmlHttp.status == 200) { The handleServerResponse function is called multiple times, whenever the status of the request changes. Only when xmlHttp.readyState is 4 will the server request be completed so you can move forward to read the results. You can also check that the HTTP transaction reported a status of 200, signaling that no problems happened during the HTTP request. When these conditions are met, you're free to read the server response and display the message to the user. 27 www.it-ebooks.info
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Page 3 and 4: AJAX and PHP Building Responsive We
Page 5 and 6: About the Authors Cristian Darie is
Page 7 and 8: About the Reviewers Emilian Balanes
Page 9 and 10: Table of Contents Preface 1 Chapter
Page 11 and 12: Table of Contents Chapter 6: AJAX S
Page 13 and 14: Preface AJAX is a complex phenomeno
Page 15 and 16: Preface What You Need for This Book
Page 17 and 18: Preface Errata Although we have tak
Page 19 and 20: 1 AJAX and the Future of Web Applic
Page 21 and 22: Chapter 1 Because end-user satisfac
Page 23 and 24: Chapter 1 Three points for you to k
Page 25 and 26: Chapter 1 With JavaScript, develope
Page 27 and 28: interrupting the user from his or h
Page 29 and 30: • Creating simple online chat sol
Page 31 and 32: Chapter 1 done typing. (This method
Page 33 and 34: Chapter 1 All exercises from this b
Page 35 and 36: etrieve the user name $name = $_GET
Page 37: Chapter 1 If you're curious to test
Page 41 and 42: 2 Client-Side Techniques with Smart
Page 43 and 44: AJAX Foundations: JavaScript and
Page 45 and 46: Chapter 2 • Because there is no s
Page 47 and 48: Time for Action—Using JavaScript
Page 49 and 50: Even More DOM In the previous exerc
Page 51 and 52: Chapter 2 What Just Happened? Well,
Page 53 and 54: Chapter 2 font-size: 10pt; } .Table
Page 55 and 56: Chapter 2 Creating the XMLHttpReque
Page 57 and 58: Chapter 2 You could, for example, c
Page 59 and 60: You will learn the most interesting
Page 61 and 62: Chapter 2 The safer version of proc
Page 63 and 64: Chapter 2 4. Create a file call
Page 65 and 66: Chapter 2 Figure 2.6: The Four HTTP
Page 67 and 68: Chapter 2 } } else { // display sta
Page 69 and 70: Chapter 2 } { // try to create XMLH
Page 71 and 72: Chapter 2 The responseXML method of
Page 73 and 74: Chapter 2 Figure 2.10: Opera Displa
Page 75 and 76: I admit that the following piece of
Page 77 and 78: 3 Server-Side Techniques with PHP a
Page 79 and 80: Chapter 3 } for (var i=0; i
Page 81 and 82: Chapter 3 // create the element $b
Page 83 and 84: Chapter 3 // create the root eleme
Page 85 and 86: Chapter 3 // read a file from the s
Page 87 and 88: Chapter 3 Figure 3.3: PHP Parameter
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Chapter 3 Without the customized er
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} } // display the error in case of
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Chapter 3 Figure 3.7: Connecting to
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Chapter 3 } } // continue only if H
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Chapter 3 You can make Firefox list
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Chapter 3 } "MSXML2.XMLHTTP.4.0", "
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'TEXT: ' . $errStr . chr(10) . 'LOC
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etrieve the parameters $num = 1; //
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Chapter 3 Figure 3.16: Flowchart De
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} Chapter 3 // only continue if xml
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} throw(response.length == 0 ? "Ser
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function process() { // ... if (req
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Chapter 3 Working with MySQL A back
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Chapter 3 Figure 3.17: Executing SQ
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Chapter 3 SELECT user_id, user_name
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3. In your foundations folder, crea
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Chapter 3 After these commands exec
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Chapter 3 • friendly.php is a PHP
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This example requires a JavaSc
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} } // try to connect to the server
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Chapter 3 } // create HTML-formatte
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Chapter 3 On the server side, all t
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4 AJAX Form Validation Validating i
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Chapter 4 Always validate user inpu
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Chapter 4 Figure 4.4: Successful Su
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Chapter 4 .left { margin-left: 150p
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Chapter 4 value="" />
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Registration Successfull! <<
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Chapter 4 } } { // display error me
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Chapter 4 require_once ('config.php
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Chapter 4 } { } $_POST['txtBthDay']
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Chapter 4 } } ?> return ($value ==
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Chapter 4 The field ID and value re
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Chapter 4 If we are dealing with cl
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5 AJAX Chat We are living in a worl
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Chapter 5 Implementing AJAX Chat We
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Chapter 5 // default the last id to
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} Chapter 5 ' DATE_FORMAT(posted_on
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Chapter 5 AJAX Chat Your b
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* function called when the Send but
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} } // retrieve the arrays from the
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Chapter 5 } } } // call server asyn
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Chapter 5 If you analyze the code f
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The business logic behind chat.php
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6 AJAX Suggest and Autocomplete Sug
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Chapter 6 The clever part of the Ja
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Chapter 6 6. Create another file na
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Chapter 6 { } a { } font-weight: bo
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Chapter 6 } { // try to create XMLH
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Chapter 6 } } } } { } displayError(
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Chapter 6 div += "" + "" + crtFunct
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} } // select the new suggestion an
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Chapter 6 } } else // FF if (oText.
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Chapter 6 Figure 6.4: PHP Documenta
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Chapter 6 We have talked about cach
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Chapter 6 visible, we need to scrol
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7 AJAX Real-Time Charting with SVG
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Chapter 7 Figure 7.1: SVG Chart The
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Chapter 7 Figure 7.2: SVG Charting
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Chapter 7 } { xmlHttp.onreadystatec
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} } // sets the X and Y attributes
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Chapter 7 } // Supported by Mozilla
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Chapter 7 • All HTTP requests go
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8 AJAX Grid Data grids have always
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Chapter 8 Figure 8.2: AJAX Grid in
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$name = $_GET['name']; // update th
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} Chapter 8 if (!isset($_SESSION['r
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Chapter 8 # editId(, true) Edit
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Chapter 8 } // this should work for
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} Chapter 8 if(editableId) editId(e
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} color: darkblue; text-align: righ
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Chapter 8 On the client, this data
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Chapter 8 save() and undo() are hel
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9 AJAX RSS Reader In the last few y
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Chapter 9 Figure 9.1: Managing RSS
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header('Pragma: no-cache'); header(
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Chapter 9 Loading feed... Abou
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Chapter 9 } // continue if the proc
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Chapter 9 } width: 410px; backgroun
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And finally, we send the HTTP reque
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10 AJAX Drag and Drop When drag-and
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Chapter 10 The Prototype features a
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Chapter 10 When dropping a task on
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Chapter 10 DROP HERE TO DELETE
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header('Expires: Fri, 25 Dec 1980 0
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Chapter 10 } } } else if (action ==
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Chapter 10 11. Load http://localhos
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details are saved using a cache sys
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Chapter 10 Summary This is it! You'
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A Preparing Your Working Environmen
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Appendix A During installation you'
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Before going through any case studi
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Appendix A Preparing Your *nix Play
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8. Finally, point your web browser
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2. Write ajax in the Create a new d
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Index A abort() method, XMLHttpRequ
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exception handling, JavaScript, 43
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PHP Parameters and Error Handling r
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updateChart() function, realTimeCha
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