AJAX and PHP

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T T Client-Side Techniques with Smarter JavaScript The third parameter of open, called async, specifies whether the request should be handled asynchronously; true means that script processing carries on after the send() method returns without waiting for a response; false means that the script waits for a response before continuing processing, freezing the web page functionality. To enable asynchronous processing, you will seed to set async to true, and handle the onreadystatechange event to process the response from the server. When using GET to pass parameters, you send the parameters using the URL's query string, as in http://localhost/ajax/test.php?param1=x&param2=y. This server request passes two parameters—a parameter called param1 with the value x, and a parameter called param2 with the value y. // call the server page to execute the server side operation xmlHttp.open("GET", "http://localhost/ajax/test.php?param1=x&param2=y", true); xmlHttp.onreadystatechange = handleRequestStateChange; xmlHttp.send(null); When using POST, you send the query string as a parameter of the send method, instead of joining it on to the base URL, like this: // call the server page to execute the server side operation xmlHttp.open("POST", "http://localhost/ajax/test.php", true); xmlHttp.onreadystatechange = handleRequestStateChange; xmlHttp.send("param1=x&param2=y"); The two code samples should have the same effects. In practice, using GET can help with debugging because you can simulate GET requests with a web browser, so you can easily see with your own eyes what your server script generates. The POST method is required when sending data larger than 512 bytes, which cannot be handled by GET. In our examples, we will place the code that makes the HTTP request inside a function called process() in the JavaScript file. The minimal implementation, which is quite fragile and doesn't implement any error-handling techniques, looks like this: function process() { // call the server page to execute the server side operation xmlHttp.open("GET", "server_script.php", true); xmlHttp.onreadystatechange = handleRequestStateChange; xmlHttp.send(null); } This method has the following potential problems: • process() may be executed even if xmlHttp doesn't contain a valid XMLHttpRequest instance. This may happen if, for example, the user's browser doesn't support XMLHttpRequest. This would cause an unhandled exception to happen, so our other efforts to handle errors don't help very much if we aren't consistent and do something about the process function as well. • process() isn't protected against other kinds of errors that could happen. For example, as you will see later in this chapter, some browsers will generate a security exception if they don't like the server you want to access with the XMLHttpRequest object (more on security in Chapter 3). 48 www.it-ebooks.info
Chapter 2 The safer version of process() looks like that: // called to read a file from the server function process() { // only continue if xmlHttp isn't void } if (xmlHttp) { // try to connect to the server } try { // initiate reading the a file from the server xmlHttp.open("GET", "server_script.php", true); xmlHttp.onreadystatechange = handleRequestStateChange; xmlHttp.send(null); } // display the error in case of failure catch (e) { alert("Can't connect to server:\n" + e.toString()); } If xmlHttp is null (or false) we don't display yet another message, as we assume a message was already displayed by the createXmlHttpRequestObject function. We make sure to display any other connection problems though. Handling Server Response When making an asynchronous request (such as in the code snippets presented earlier), the execution of xmlHttp.send() doesn't freeze until the server response is received; instead, the execution continues normally. The handleRequestStateChange method is the callback method that we set to handle request state changes. Usually this is called four times, for each time the request enters a new stage. Remember the readyState property can be any of the following: 0 = uninitialized 1 = loading 2 = loaded 3 = interactive 4 = complete Except state 3, all the others are pretty self-explaining names. The interactive state is an intermediate state when the response has been partially received. In our AJAX applications we will only use the complete state, which marks that a response has been received from the server. The typical implementation of handleRequestStateChange is shown in the following code snippet, which highlights the portion where you actually get to read the response from the server: // function executed when the state of the request changes function handleRequestStateChange() { // continue if the process is completed if (xmlHttp.readyState == 4) { // continue only if HTTP status is "OK" if (xmlHttp.status == 200) { // retrieve the response response = xmlHttp.responseText; 49 www.it-ebooks.info
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AJAX and PHP Building Responsive We
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About the Authors Cristian Darie is
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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 and 38: Chapter 1 If you're curious to test
Page 39 and 40: Chapter 1 request. In our case, thi
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: You will learn the most interesting
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
Page 89 and 90: Chapter 3 Without the customized er
Page 91 and 92: } } // display the error in case of
Page 93 and 94: Chapter 3 Figure 3.7: Connecting to
Page 95 and 96: Chapter 3 } } // continue only if H
Page 97 and 98: Chapter 3 You can make Firefox list
Page 99 and 100: Chapter 3 } "MSXML2.XMLHTTP.4.0", "
Page 101 and 102: 'TEXT: ' . $errStr . chr(10) . 'LOC
Page 103 and 104: etrieve the parameters $num = 1; //
Page 105 and 106: Chapter 3 Figure 3.16: Flowchart De
Page 107 and 108: } Chapter 3 // only continue if xml
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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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