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Learn JavaScript the quick and easy way, from the experts at w3schools There’s no faster, easier way to learn JavaScript and Ajax You will learn: • What JavaScript is and isn’t • How to put JavaScript into an HTML page • JavaScript special characters and guidelines • How to use JavaScript operators • If…else statements and do…while loops Learn JavaScript ® and Ajax with w3schools ® Learn JavaScript and Ajax If you want to start building interactive Web pages right away, you should begin by learning how to use JavaScript and Ajax. w3schools has perfected a straightforward tutorial approach that gives you what you need to know in manageable lessons, liberally supported with examples. You’ll find that tried-and-true format in this book, along with a detailed reference section that you will use again and again. • All about JavaScript objects • How to use Ajax properties • What the Ajax XMLHttpRequest Object does $29.99 US/$35.99 CAN with w3schools w3schools is a leading Web destination for learning key Web technologies online. Founded in 1999, it receives more than 10 million unique visitors each month. w3schools tutorials are required reading in more than 100 high schools and universities. Add JavaScript Define functions Create cookies Declare variables Create objects Build Ajax pages Programming Languages/ JavaScript 611944-Ch01.F.indd 8 4/20/10 1:35 PM Learn JavaScript ® and AJAX with w3schools Hege Refsnes, Ståle Refsnes, Kai Jim Refsnes, and Jan Egil Refsnes with Kelly Dobbs Henthorne Wiley Publishing, Inc. 611944-FM.F.indd 1 4/29/10 9:47 PM Learn JavaScript and AJAX with w3schools ® Published by Wiley Publishing, Inc. 111 River Street Hoboken, NJ 07030-5774 www.wiley.com Copyright © 2010 by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada ISBN: 978-0-470-61194-4 LOC/CIP: 2010925161 Manufactured in the United States of America 10 9 8 7 6 5 4 3 2 1 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, N 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permissions. Limit of Liability/Disclaimer of Warranty: The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales or promotional materials. The advice and strategies contained herein may not be suitable for every situation. This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If professional assistance is required, the services of a competent professional person should be sought. Neither the publisher nor the author shall be liable for damages arising herefrom. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. For general information on our other products and services please contact our Customer Care Department within the United States at (877) 762-2974, outside the United States at (317) 5723993 or fax (317) 572-4002. Trademarks: Wiley, the Wiley logo, and related trade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates, in the United States and other countries, and may not be used without written permission. w3schools and the w3schools logo are registered trademarks of w3schools. JavaScript is a registered trademark of Sun Microsystems, Inc. All other trademarks are the property of their respective owners. Wiley Publishing, Inc., is not associated with any product or vendor mentioned in this book. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress CIP Data is available from the publisher. 611944-FM.F.indd 2 4/29/10 9:47 PM w3schools Authors/Editors w3schools’ mission is to publish well-organized and easy-to-understand online tutorials based on the W3C Web standards. Hege Refsnes Hege is a writer and editor for w3schools. She works to improve the usability and accessibility of the Web. Hege has been writing tutorials for w3schools since 1998. Ståle Refsnes Ståle has ten years of Internet development experience, developing all the Web-based solutions for The Norwegian Handball Federation. Ståle has been writing tutorials for w3schools since 1999. Kai Jim Refsnes Kai Jim has been around computers since childhood, working with them since the age of 14. He has been writing tutorials for w3schools since completing a bachelor’s degree in information technology in 2005. Jan Egil Refsnes Jan Egil is the president and founder of w3schools. He is a senior system developer with a master’s degree in information technology and more than 30 years of computing experience. “Jani” has supervised a large number of company-critical development projects for oil companies like Amoco, British Petroleum, ELF, Halliburton, and Brown & Root. He has also developed computer-based solutions for more than 20 governmental institutions like The National Library, Norwegian High Schools, The State Hospital, and many others. Jani started w3schools in 1998. 611944-FM.F.indd 3 4/29/10 9:47 PM Credits Acquisitions Editor Scott Meyers Production Abshier House Technical Editor Harry Buss Copy Editor Abshier House Associate Director of Marketing David Mayhew Production Manager Tim Tate 611944-FM.F.indd 4 Vice President and Executive Group Publisher Richard Swadley Vice President and Executive Publisher Barry Pruett Associate Publisher Jim Minatel Project Coordinator, Cover Lynsey Stanford Proofreading and Indexing Abshier House Cover Designer Michael Trent 4/29/10 9:47 PM Table of Contents Introduction..................................................1 JavaScript............................................................................................ 1 AJAX................................................................................................... 3 How To Use This Book....................................................................... 4 Section I: JavaScript Basic..............................7 Chapter 1: JavaScript How To and Where To............... 9 How To Put a JavaScript into an HTML Page..................................... 9 How to Handle Simple Browsers....................................................... 12 Where to Put the JavaScript.............................................................. 12 Using an External JavaScript............................................................. 15 Chapter 2: JavaScript Statements and Comments....... 16 JavaScript Statements........................................................................ 16 JavaScript Comments........................................................................ 18 Chapter 3: JavaScript Variables................................... 23 Do You Remember Algebra from School?.......................................... 23 JavaScript Variables........................................................................... 23 Declaring (Creating) JavaScript Variables.......................................... 25 Assigning Values to Undeclared JavaScript Variables.......................... 25 Redeclaring JavaScript Variables........................................................ 26 JavaScript Arithmetic........................................................................ 26 v 611944-FM.F.indd 5 4/29/10 9:47 PM Table of Contents Chapter 4: JavaScript Operators................................. 27 JavaScript Arithmetic Operators........................................................ 27 JavaScript Assignment Operators....................................................... 28 The + Operator Used on Strings........................................................ 28 Adding Strings and Numbers............................................................ 28 Chapter 5: JavaScript Comparisons............................ 30 Comparison Operators...................................................................... 30 How to Use Comparisons................................................................. 31 Logical Operators.............................................................................. 31 Conditional Operator....................................................................... 31 Chapter 6: JavaScript If...Else Statements................... 32 Conditional Statements..................................................................... 32 if Statement....................................................................................... 33 if...else Statement.............................................................................. 34 if...else if...else Statement................................................................... 36 Chapter 7: JavaScript Loops....................................... 39 The for Loop..................................................................................... 39 The while Loop................................................................................. 41 The do...while Loop.......................................................................... 43 Chapter 8: Additional JavaScript Flow Control Statements.................................................................... 46 The break Statement......................................................................... 46 The continue Statement.................................................................... 47 JavaScript for...in Statement.............................................................. 48 JavaScript switch Statement............................................................... 50 vi 611944-FM.F.indd 6 4/29/10 9:47 PM Table of Contents Chapter 9: JavaScript Popup Boxes............................. 53 Popup Boxes...................................................................................... 53 Chapter 10: JavaScript Functions............................... 58 How to Define a Function................................................................ 58 JavaScript Function Examples........................................................... 59 The return Statement........................................................................ 62 The Lifetime of JavaScript Variables.................................................. 63 Chapter 11: JavaScript Events..................................... 64 onLoad and onUnload...................................................................... 64 onFocus, onBlur, and onChange....................................................... 65 onSubmit.......................................................................................... 65 onMouseOver and onMouseOut....................................................... 66 onClick............................................................................................. 66 Chapter 12: Javascript try…catch and throw Statements.......................................................... 67 JavaScript—Catching Errors............................................................. 67 The try...catch Statement.................................................................. 67 The throw Statement......................................................................... 70 Chapter 13: JavaScript Special Characters and Guidelines.................................................................... 73 Insert Special Characters................................................................... 73 JavaScript Is Case Sensitive................................................................ 74 White Space...................................................................................... 74 Break up a Code Line........................................................................ 74 vii 611944-FM.F.indd 7 4/29/10 9:47 PM Table of Contents Section II: JavaScript Objects.......................77 Chapter 14: JavaScript Objects Intro.......................... 79 Object-Oriented Programming......................................................... 79 Properties.......................................................................................... 79 Methods............................................................................................ 80 Chapter 15: JavaScript String Object.......................... 81 String Object..................................................................................... 81 Examples........................................................................................... 82 Chapter 16: JavaScript Date Object............................ 88 Create a Date Object......................................................................... 88 Set Dates........................................................................................... 89 Compare Two Dates.......................................................................... 89 Examples........................................................................................... 90 Chapter 17: JavaScript Array Object........................... 95 What Is an Array?.............................................................................. 95 Create an Array................................................................................. 96 Access an Array................................................................................. 96 Modify Values in an Array................................................................. 96 Examples........................................................................................... 97 Chapter 18: JavaScript Boolean Object.................... 107 Create a Boolean Object.................................................................. 107 Examples......................................................................................... 108 viii 611944-FM.F.indd 8 4/29/10 9:47 PM Table of Contents Chapter 19: JavaScript Math Object......................... 110 Math Object................................................................................... 110 Mathematical Constants.................................................................. 110 Mathematical Methods................................................................... 111 Examples......................................................................................... 112 Chapter 20: JavaScript RegExp Object..................... 115 What Is RegExp?............................................................................. 115 RegExp Modifiers............................................................................ 116 test()................................................................................................ 118 exec().............................................................................................. 119 Section III: JavaScript Advanced.................121 Chapter 21: JavaScrip Browser Detection................. 123 Browser Detection........................................................................... 123 The Navigator Object..................................................................... 124 Chapter 22: JavaScript Cookies................................ 129 What Is a Cookie?........................................................................... 129 Create and Store a Cookie............................................................... 130 Chapter 23: JavaScript Form Validation................... 134 Required Fields............................................................................... 134 E-mail Validation............................................................................ 136 ix 611944-FM.F.indd 9 4/29/10 9:47 PM Table of Contents Chapter 24: JavaScript Animation............................ 138 The HTML Code........................................................................... 138 The JavaScript Code........................................................................ 139 The Entire Code............................................................................. 139 Chapter 25: JavaScript Image Maps.......................... 141 HTML Image Maps........................................................................ 141 Adding Some JavaScript.................................................................. 142 Chapter 26: JavaScript Timing Events...................... 144 The setTimeout() Method............................................................... 144 The clearTimeout() Method............................................................ 149 Chapter 27: Create Your Own Objects with JavaScript............................................................ 151 JavaScript Objects........................................................................... 151 Creating Your Own Objects............................................................ 152 Section IV: AJAX Basic................................157 Chapter 28: AJAX XMLHttpRequest....................... 159 AJAX Uses the XMLHttpRequest Object........................................ 159 The XMLHttpRequest Object........................................................ 159 Your First AJAX Application........................................................... 160 Chapter 29: AJAX Browser Support......................... 163 The XMLHttpRequest.................................................................... 163 All Together Now............................................................................ 164 x 611944-FM.F.indd 10 4/29/10 9:47 PM Table of Contents Chapter 30: AJAX—The XMLHttpRequest Object’s Methods and Properties................................. 166 Important Methods......................................................................... 166 Sending an AJAX Request to a Server.............................................. 167 Important Properties....................................................................... 167 The responseText Property.............................................................. 167 XMLHttpRequest Open—Using False............................................ 167 XMLHttpRequest Open—Using True............................................ 168 The readyState Property.................................................................. 168 The onreadystatechange Property.................................................... 169 Chapter 31: AJAX Server.......................................... 170 XMLHttpRequest Object Can Request Any Data........................... 170 Requesting Files.............................................................................. 170 Submitting Forms........................................................................... 171 Section V: AJAX Advanced.........................173 Chapter 32: AJAX Suggest....................................... 175 The HTML Form........................................................................... 175 The showHint() Function............................................................... 176 The GetXmlHttpObject() Function................................................ 177 The stateChanged() Function.......................................................... 177 AJAX Suggest Source Code............................................................. 178 Chapter 33: AJAX Database Example....................... 184 The AJAX JavaScript....................................................................... 185 The AJAX Server Page..................................................................... 186 xi 611944-FM.F.indd 11 4/29/10 9:47 PM Table of Contents Chapter 34: AJAX XML Example............................ 188 The AJAX JavaScript....................................................................... 189 The AJAX Server Page..................................................................... 190 The XML File................................................................................. 191 Chapter 35: AJAX ResponseXML Example.............. 198 The AJAX JavaScript....................................................................... 199 The AJAX Server Page..................................................................... 201 Appendixes...............................................203 Appendix A: JavaScript Objects........................................................................203 Appendix B: HTML DOM Objects.................................................................214 Index.........................................................245 xii 611944-FM.F.indd 12 4/29/10 9:47 PM Introduction W elcome to Learn JavaScript and Ajax with w3schools. This book is for Web site designers and builders who want to learn to add interactivity to their Web pages with JavaScript and Ajax. w3schools (www.w3schools.com), is one of the top Web destinations to learn JavaScript and many other key Web languages. Founded in 1998, w3schools’ tutorials are recommended reading in more than 100 universities and high schools all over the world. This book is a great companion to the JavaScript and Ajax tutorials on the w3schools site, which were written by Jan Egil Refsnes, Ståle Refsnes, Kai Jim Refsnes, and Hege Refsnes. Like the w3schools online tutorials, this book features a brief presentation of each topic, trading lengthy explanations for abundant examples showcasing each key feature. This book, as well as other w3schools books published by Wiley, features straight-forward and concise tutorials on each topic from which the beginning Web developer can easily learn. All of the book’s content is derived from w3schools’ accurate, user-tested content used by millions of learners every month. JavaScript JavaScript is the scripting language of the Web. JavaScript is used in millions of Web pages to add functionality, validate forms, detect browsers, and much more. JavaScript is the most popular scripting language on the Internet and works in all major browsers, such as Internet Explorer, Firefox, Chrome, Opera, and Safari. What You Should Already Know Before you continue you should have a basic understanding of HTML. If you want to study this subject first, please read Learn HTML and CSS with w3schools. What Is JavaScript? 8 JavaScript was designed to add interactivity to HTML pages. 8 JavaScript is a scripting language. 8 A scripting language is a lightweight programming language. 8 JavaScript is usually embedded directly into HTML pages. 611944-FM.F.indd 1 4/29/10 9:47 PM Learn JavaScript and AJAX with w3schools 8 JavaScript is an interpreted language (means that scripts execute without preliminary compilation). 8 Everyone can use JavaScript without purchasing a license. Are Java and JavaScript the Same? No, they are not. Java and JavaScript are two completely different languages in both concept and design. Java (developed by Sun Microsystems) is a powerful and much more complex programming language in the same category as C and C++. What Can JavaScript Do? 8 JavaScript gives HTML designers a programming tool. HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax. Almost anyone can put small “snippets” of code into their HTML pages. 8 JavaScript can put dynamic text into an HTML page. A JavaScript statement like document.write(“

” + name + “

”) can write a variable text into an HTML page. 8 JavaScript can react to events. A JavaScript script can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element. 8 JavaScript can read and write HTML elements. A JavaScript script can read and change the content of an HTML element. 8 JavaScript can be used to validate data. A JavaScript script can be used to validate form data before it is submitted to a server. This saves the server from extra processing. 8 JavaScript can be used to detect the visitor’s browser. A JavaScript script can be used to detect the visitor’s browser, and depending on the browser, load another page specifically designed for that browser. 8 JavaScript can be used to create cookies. A JavaScript script can be used to store and retrieve information on the visitor’s computer. The Real Name Is ECMAScript JavaScript’s official name is ECMAScript, which is developed and maintained by the ECMA International organization. The language was invented by Brendan Eich at Netscape (with Navigator 2.0) and has appeared in all Netscape and Microsoft browsers since 1996. 2 611944-FM.F.indd 2 4/29/10 9:47 PM Introduction ECMA-262 is the official JavaScript standard. The development of ECMA-262 started in 1996, and the first edition of was adopted by the ECMA General Assembly in June 1997. The standard was approved as an international ISO (ISO/IEC 16262) standard in 1998. The development of the standard is still in progress. AJAX AJAX equals Asynchronous JavaScript and XML. AJAX is based on JavaScript and HTTP requests. AJAX is not a new programming language, but a new way to use existing standards. AJAX is the art of trading data with a Web server, and changing parts of a Web page, without reloading the whole page. What You Should Already Know Before you continue you should have a basic understanding of the following: 8 HTML 8 JavaScript If you want to study these subjects first, find the tutorials on the w3schools home page. AJAX = Asynchronous JavaScript and XML AJAX is not a new programming language, but a new technique for creating better, faster, and more interactive Web applications. With AJAX, a JavaScript can communicate directly with the server, with the XMLHttpRequest object. With this object, a JavaScript can trade data with a Web server, without reloading the page. AJAX uses asynchronous data transfer (HTTP requests) between the browser and the Web server, allowing Web pages to request small bits of information from the server instead of whole pages. The AJAX technique makes Internet applications smaller, faster, and more user friendly. AJAX Is Based on Internet Standards AJAX is based on the following Web standards: 8 JavaScript 8 XML 3 611944-FM.F.indd 3 4/29/10 9:47 PM Learn JavaScript and AJAX with w3schools 8 HTML 8 CSS AJAX applications are browser- and platform-independent. AJAX Is About Better Internet-Applications Internet applications have many benefits over desktop applications: They can reach a larger audience; they are easier to install and support; and they are easier to develop. However, Internet applications are not always as “rich” and user friendly as traditional desktop applications. With AJAX, Internet applications can be made richer and more user friendly. Start Using AJAX Today There is nothing new to learn. AJAX is based on existing standards. These standards have been used by developers for several years. How To Use This Book Throughout this book, you will see several icons: Try it yourself >> The Try It Yourself icon indicates an opportunity for you to practice what you’ve just learned. The code and examples under this icon come from examples on the w3schools site, which allow you to make changes to the code and see the results immediately. You do not have to type in the code examples in this book; you will find them all on the w3schools site.  he w3schools icon indicates that more information is available on the w3schools T site. This icon indicates where you will find further information about a topic that is covered more thoroughly elsewhere within the book. This book is divided into five sections: 8 Section I: JavaScript Basic 8 Section II: JavaScript Objects 8 Section III: JavaScript Advanced 8 Section IV: AJAX Basic 8 Section V: SectionAJAX Advanced 4 611944-FM.F.indd 4 4/29/10 9:47 PM Introduction If you’re anxious to improve your Web pages and to add some interactivity, jump right in with JavaScript Basic. Plenty of examples and opportunities to try things await, and w3schools will be right there when you need them! 5 611944-FM.F.indd 5 4/29/10 9:47 PM 611944-FM.F.indd 6 4/29/10 9:47 PM Section I JavaScript Basic ❑ Chapter 1: JavaScript How To and Where To ❑ Chapter 2: JavaScript Statements and Comments ❑ Chapter 3: JavaScript Variables ❑ Chapter 4: JavaScript Operators ❑ Chapter 5: JavaScript Comparisons ❑ Chapter 6: JavaScript If…Else ❑ Chapter 7: JavaScript Loops ❑ Chapter 8: JavaScript Flow Control Statements ❑ Chapter 9: JavaScript Switch and Popup Boxes ❑ Chapter 10: JavaScript Functions ❑ Chapter 11: JavaScript Events ❑ Chapter 12: JavaScript Try…Catch and Throw Statements ❑ Chapter 13: JavaScript Special Characters and Guidelines 7 611944-Ch01.F.indd 7 4/20/10 1:35 PM 611944-Ch01.F.indd 8 4/20/10 1:35 PM Chapter 1 JavaScript How To and Where To In This Chapter ❑ How To Put a JavaScript into an HTML Page ❑ How To Handle Simple Browsers ❑ Where To Put the JavaScript ❑ Using an External JavaScript The HTML Figure 1.1 9 611944-Ch01.F.indd 9 4/20/10 1:35 PM Learn JavaScript and Ajax with w3schools Here’s your first opportunity to personalize JavaScript. Change the “Hello World” text to “Happy, Happy, Joy, Joy!” and see what happens. The result of your changes is shown in Figure 1.2. Try it yourself >> Figure 1.2 The following example shows how to add HTML tags to the JavaScript. The result of this code is shown in Figure 1.3. Figure 1.3 Continuing with our happier version of the code, change the “Hello World!” text to “Happy, Happy, Joy, Joy!” and see what happens. The result of your changes is shown in Figure 1.4. 10 611944-Ch01.F.indd 10 4/20/10 1:35 PM Chapter 1: JavaScript How To and Where To Try it yourself >> Figure 1.4 To insert a JavaScript into an HTML page, we use the tell where the JavaScript starts and ends: The document.write command is a standard JavaScript command for writing output to a page. When you type the document.write command between the NOTE If we had not typed the The two forward slashes at the end of comment line (//) comprise the JavaScript comment symbol. This prevents JavaScript from executing the --> tag. Where to Put the JavaScript JavaScripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, or at a later event, such as when a user clicks a button. When this is the case we put the script inside a function. You will learn about functions in Chapter 10, “JavaScript Functions.” 12 611944-Ch01.F.indd 12 4/20/10 1:35 PM Chapter 1: JavaScript How To and Where To Scripts in Scripts to be executed when they are called, or when an event is triggered, are placed in functions. Put your functions in the head section. This way they are all in one place, and they do not interfere with page content. The resulting alert box is shown in Figure 1.6. Try it yourself >> Figure 1.6 Scripts in If you don’t want your script to be placed inside a function, or if your script should write page content, it should be placed in the body section. Figure 1.7 shows the result. 13 611944-Ch01.F.indd 13 4/20/10 1:35 PM Learn JavaScript and Ajax with w3schools Try it yourself >> Figure 1.7 Scripts in and You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section. 14 611944-Ch01.F.indd 14 4/20/10 1:35 PM Chapter 1: JavaScript How To and Where To Using an External JavaScript If you want to run the same JavaScript on several pages without having to write the same script on every page, you can write a JavaScript in an external file. Save the external JavaScript file with a .js file extension. Your results are shown in Figure 1.8. NOTE The external script cannot contain the Figure 1.8 NOTE Remember to place the script exactly where you normally would write the script! 15 611944-Ch01.F.indd 15 4/20/10 1:35 PM Chapter 2 JavaScript Statements and Comments In This Chapter ❑ JavaScript Code ❑ JavaScript Blocks ❑ JavaScript Multiline Comments ❑ Using Comments To Prevent Execution ❑ Using Comments at the End of a Line JavaScript is a sequence of statements to be executed by the browser. Unlike HTML, JavaScript is case-sensitive; therefore, watch your capitalization closely when you write JavaScript statements and create or call variables, objects, and functions. JavaScript Statements A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do. The following JavaScript statement tells the browser to write “Hello Dolly” to the Web page: document.write("Hello Dolly"); It is normal to add a semicolon at the end of each executable statement. Most people think this is a good programming practice, and most often you will see this in JavaScript examples on the Web. The semicolon is optional (according to the JavaScript standard), and the browser is supposed to interpret the end of the line as the end of the statement. You often will see examples without the semicolon at the end. 16 611944-Ch02.F.indd 16 4/20/10 1:34 PM Chapter 2: JavaScript Statements and Comments NOTE Using semicolons makes it possible to write multiple statements on one line, although good programming practice encourages placing only one statement per line. JavaScript Code JavaScript code (or just JavaScript) is a sequence of JavaScript statements. Each statement is executed by the browser in the sequence it is written. This example will write a heading and two paragraphs to a Web page as shown in Figure 2.1. Try it yourself >> Figure 2.1 JavaScript Blocks JavaScript statements can be grouped together in blocks. Blocks start with a left curly bracket { and end with a right curly bracket }. The purpose of a block is to make the sequence of statements execute together. The following example writes a heading and two paragraphs to a Web page as shown in Figure 2.2. 17 611944-Ch02.F.indd 17 4/20/10 1:34 PM Learn JavaScript and Ajax with w3schools Try it yourself >> Figure 2.2 The preceding example is not very useful. It just demonstrates the use of a block. Normally, a block is used to group statements together in a function or in a condition (in which a group of statements should be executed if a condition is met). You will learn more about functions and conditions in Chapters 6 and 10. JavaScript Comments JavaScript comments can be added to explain the JavaScript script or to make the code more readable. Single line comments start with //. The following example uses single-line comments to explain the code. 18 611944-Ch02.F.indd 18 4/20/10 1:34 PM Chapter 2: JavaScript Statements and Comments Your result is shown in Figure 2.3. Try it yourself >> Figure 2.3 JavaScript Multiline Comments Multiline comments start with /* and end with */. The following example uses a multiline comment to explain the code. Your result is shown in Figure 2.4. Try it yourself >> Figure 2.4 Using Comments to Prevent Execution In the following example, the comment is used to prevent the execution of a single code line (can be suitable for debugging): Your result is shown in Figure 2.5. Try it yourself >> Figure 2.5 In the following example, the comment is used to prevent the execution of a code block (can be suitable for debugging): Try it yourself >> Your result would be a blank screen. 21 611944-Ch02.F.indd 21 4/20/10 1:34 PM Learn JavaScript and Ajax with w3schools Using Comments at the End of a Line In the following example, the comment is placed at the end of a code line. Your result is shown in Figure 2.6. Try it yourself >> Figure 2.6 22 611944-Ch02.F.indd 22 4/20/10 1:34 PM Chapter 3 JavaScript Variables In This Chapter ❑ Do You Remember Algebra from School? ❑ JavaScript Variables ❑ Declaring (Creating) JavaScript Variables ❑ Assigning Values to Undeclared JavaScript Variables ❑ Redeclaring JavaScript Variables ❑ JavaScript Arithmetic Variables are “containers” for storing information. Do You Remember Algebra from School? Do you remember algebra from school? x = 5, y = 6, z = x + y Do you remember that a letter (like x) could be used to hold a value (like 5), and that you could use the information given to calculate the value of z to be 11? These letters are called variables. Variables can be used to hold values (x = 5) or expressions (z = x + y). JavaScript Variables As with algebra, JavaScript variables are used to hold values or expressions. A variable can have a short name, like x, or a more descriptive name, like carname. 23 611944-Ch03.F.indd 23 4/20/10 1:35 PM Learn JavaScript and Ajax with w3schools Rules for JavaScript variable names: 8 Variable names are case sensitive (y and Y are two different variables). 8 Variable names must begin with a letter, the underscore character, or a dollar sign. (The $ character is used primarily by code-generation tools.) 8 Subsequent characters may be letter, number, underscore, or dollar sign. N O TE TIP There are 59 reserved words that are not legal variable names. Because JavaScript is case sensitive, variable names are case sensitive. A variable’s value can change during the execution of a script. You can refer to a variable by its name to display or change its value. Your result is shown in Figure 3.1. Try it yourself >>

The script above declares a variable, assigns a value to it, displays the value, changes the value,and displays the value again.

24 611944-Ch03.F.indd 24 4/20/10 1:35 PM Chapter 3: Javascript Variables Figure 3.1 Declaring (Creating) JavaScript Variables Creating variables in JavaScript is most often referred to as “declaring” variables. You can declare JavaScript variables with the var statement: var x; var carname; After the declaration shown, the variables are empty. (They have no values yet.) However, you can also assign values to the variables when you declare them: var x=5; var carname="Volvo"; After the execution of the preceding statements, the variable x will hold the value 5, and carname will hold the value Volvo. N O TE When you assign a text value to a variable, use quotes around the value. Assigning Values to Undeclared JavaScript Variables If you assign values to variables that have not yet been declared, the variables will automatically be declared. The following statements: x=5; carname="Volvo"; (continued) 25 611944-Ch03.F.indd 25 4/20/10 1:35 PM Learn JavaScript and Ajax with w3schools (continued) have the same effect as these: var x=5; var carname="Volvo"; Redeclaring JavaScript Variables If you redeclare a JavaScript variable, it will not lose its original value. var x=5; var x; After the execution of the preceding statements, the variable x will still have the value of 5. The value of x is not reset (or cleared) when you redeclare it. JavaScript Arithmetic As with algebra, you can do arithmetic operations with JavaScript variables: y=x-5; z=y+5; N O TE Sometimes the results seem unpredictable. If at least one variable on the right side of an assignment expression contains a string value, the result will be a string and the “+” operator is applied as the concatenation operator to the toString() values of the variables. Only if all the variables to the right of the assignment operator are numbers will the result be a number. You will learn more about the operators that can be used in Chapter 4, “JavaScript Operators.” 26 611944-Ch03.F.indd 26 4/20/10 1:35 PM Chapter 4 JavaScript Operators In This Chapter ❑ JavaScript Arithmetic Operators ❑ JavaScript Assignment Operators ❑ The + Operator Used on Strings ❑ Adding Strings and Numbers The assignment operator, =, is used to assign values to JavaScript variables, as shown in the first two lines of the following code. The arithmetic operator, +, is used to add values together, as shown in the last line of the following code. y = 5; z = 2; x = y+z; The value of x, after the execution of the preceding statements is 7. JavaScript Arithmetic Operators Arithmetic operators are used to perform arithmetic between variables and/or values. Given that y = 5, the following table explains the arithmetic operators. Operator + * / % ++ -- Description Addition Subtraction Multiplication Division Modulus (division remainder) Increment Decrement Example x = y+2 x = y-2 x = y*2 x = y/2 x = y%2 x = ++y x = --y Result x=7 x=3 x = 10 x = 2.5 x=1 x=6 x=4 27 611944-Ch04.F.indd 27 4/20/10 1:36 PM Learn JavaScript and Ajax with w3schools JavaScript Assignment Operators Assignment operators are used to assign values to JavaScript variables. Given that x = 10 and y = 5, the following table explains the assignment operators: Operator = += -= *= /= %= Example x=y x+ = y x- = y x* = y x/ = y x% = y Same As   x = x+y x = x-y x = x*y x = x/y x = x%y Result x=5 x = 15 x=5 x = 50 x=2 x=0 The + Operator Used on Strings The + operator also can be used to concatenate string variables or text values together. To concatenate two or more string variables together, use the + operator: txt1="What a very"; txt2="nice day"; txt3=txt1+txt2; After the execution of the preceding statements, the variable txt3 contains “What a verynice day”. To add a space between the two strings, insert a space into one of the strings: txt1="What a very "; txt2="nice day"; txt3=txt1+txt2; Or insert a space into the expression: txt1="What a very"; txt2="nice day"; txt3=txt1+" "+txt2; After the execution of the preceding statements, the variable txt3 contains: “What a very nice day” Adding Strings and Numbers The rule is as follows: If you add a number and a string, the result will be a string! Your results are shown in Figure 4.1. 28 611944-Ch04.F.indd 28 4/20/10 1:36 PM Chapter 4: Javascript Operators Try it yourself >>

The rule is: If you add a number and a string, the result will be a string.

Figure 4.1 29 611944-Ch04.F.indd 29 4/20/10 1:36 PM Chapter 5 JavaScript Comparisons In This Chapter ❑ Comparison Operators ❑ How to Use Comparisons ❑ Logical Operators ❑ Conditional Operator Comparison and logical operators are used to test for true or false. Comparison Operators Comparison operators are used in logical statements to determine equality or difference between variables or values. Given that x = 5, the following table explains the comparison operators: Operator == === Description is equal to value...is equal to value is exactly equal to value and type != > < >= <= is not equal is greater than is less than is greater than or equal to is less than or equal to Example x == 8 is false x === 5 is true x === “5” is false x! = 8 is true x > 8 is false x < 8 is true x >= 8 is false x <= 8 is true 30 611944-Ch05.F.indd 30 4/20/10 1:36 PM Chapter 5: Javascript Comparisons How to Use Comparisons Comparison operators can be used in conditional statements to compare values and take action depending on the result: if (age<18) document.write("Too young"); You will learn more about the use of conditional statements in the next chapter. Logical Operators Logical operators are used to determine the logic between variables or values. Given that x = 6 and y = 3, the following table explains the logical operators: Operator && || ! Description and or not Example (x < 10 && y > 1) is true (x == 5 || y == 5) is false !(x == y) is true Conditional Operator JavaScript also contains a conditional operator that assigns a value to a variable based on some condition. The syntax is as follows: variablename=(condition)?value1:value2 For example, greeting=(visitor=="PRES")?"Dear President ":"Dear "; If the variable visitor has the value of "PRES", then the variable greeting will be assigned the value "Dear President " else it will be assigned "Dear". 31 611944-Ch05.F.indd 31 4/20/10 1:36 PM Chapter 6 JavaScript If...Else Statements In This Chapter ❑ Conditional Statements ❑ if Statement ❑ if...else Statement ❑ if...else if...else Statement Conditional statements are used to perform different actions based on different conditions. Conditional Statements Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this. JavaScript has the following conditional statements: 8 if statement. Use this statement to execute some code only if a specified condition is true. 8 if...else statement. Use this statement to execute some code if the condition is true and another code if the condition is false. 8 if...else if....else statement. Use this statement to select one of many blocks of code to be executed. 8 switch statement. Use this statement to select one of many blocks of code to be executed. 32 611944-Ch06.F.indd 32 4/20/10 1:37 PM Chapter 6: JavaScript If...Else Statements TIP With conditionals, a { } block must contain the statements to be executed. If curly braces are not present, only the subsequent statement is executed, which is a very common programming error. if (condition) { statement 1; statement 2; statement 3; } // all three statements are executed if (condition) statement 1; statement 2; statement 3; // only statement 1 is executed if Statement Use the if statement to execute some code only if a specified condition is true. The syntax is as follows: if (condition) { code to be executed if condition is true } Your result is shown in Figure 6.1. TIP if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error! Try it yourself >>

This example demonstrates the If statement.

If the time on your browser is less than 10, you will get a "Good morning" greeting.

Figure 6.1 N O TE There is no ..else.. in this syntax. You tell the browser to execute some code only if the specified condition is true. if...else Statement Use the if....else statement to execute some code if a condition is true and another code if the condition is not true. The syntax is as follows: if (condition) { code to be executed if condition is true } else { code to be executed if condition is not true } 34 611944-Ch06.F.indd 34 4/20/10 1:37 PM Chapter 6: JavaScript If...Else Statements Try it yourself >>

This example demonstrates the If...Else statement.

If the time on your browser is less than 10, you will get a "Good morning" greeting. Otherwise you will get a "Good day" greeting.

Your result is shown in Figure 6.2. Figure 6.2 35 611944-Ch06.F.indd 35 4/20/10 1:37 PM Learn JavaScript and Ajax with w3schools The following example demonstrates a random link. When you click on the link, it will take you to w3schools.com OR to RefsnesData.no. There is a 50 percent chance for each of them. Your result is shown in Figure 6.3. Try it yourself >> Figure 6.3 if...else if...else Statement Use the if....else if...else statement to select one of several blocks of code to be executed. The syntax is as follows: if (condition1) { code to be executed if condition1 is true 36 611944-Ch06.F.indd 36 4/20/10 1:37 PM Chapter 6: JavaScript If...Else Statements } else if (condition2) { code to be executed if condition2 is true } else { code to be executed if condition1 and condition2 are not true } Your result is shown in Figure 6.4. Try it yourself >>

This example demonstrates the if..else if...else statement.

(continued) 37 611944-Ch06.F.indd 37 4/20/10 1:37 PM Learn JavaScript and Ajax with w3schools (continued) Figure 6.2 \ 38 611944-Ch06.F.indd 38 4/20/10 1:37 PM Chapter 7 JavaScript Loops In This Chapter ❑ The for Loop ❑ The while Loop ❑ The do...while Loop Loops execute a block of code a specified number of times or while a specified condition is true. Often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal lines in a script, you can use loops to perform a task like this. In JavaScript, there are two kinds of loops: 8 for. Loops through a block of code a specified number of times 8 while. Loops through a block of code while a specified condition is true The for Loop The for loop is used when you know in advance how many times the script should run. The syntax is as follows: for (var=startvalue;var<=endvalue;var=var+increment) { code to be executed } The following example defines a loop that starts with i = 0. The loop will continue to run as long as i is less than or equal to 5. i will increase by 1 each time the loop runs. Your result is shown in Figure 7.1. N OTE The increment parameter could also be negative, and the <= could be any comparing statement. 39 611944-Ch07.F.indd 39 4/20/10 1:38 PM Learn JavaScript and Ajax with w3schools Try it yourself >>

Explanation:

This for loop starts with i=0.

As long as i is less than, or equal to 5, the loop will continue to run.

i will increase by 1 each time the loop runs.

Figure 7.1 40 611944-Ch07.F.indd 40 4/20/10 1:38 PM Chapter 7: Javascript Loops In the following example, you loop through the six different HTML headings. Your result is shown in Figure 7.2. Try it yourself >> Figure 7.2 The while Loop The while loop loops through a block of code a specified number of times or while a specified condition is true. The syntax is as follows: while (var<=endvalue) { (continued) 41 611944-Ch07.F.indd 41 4/20/10 1:38 PM Learn JavaScript and Ajax with w3schools (continued) code to be executed } N OTE The <= could be any comparing statement. TIP The distinction between the for and the while is that in the for loop, the conditions are known and can be specified beforehand. The while loop is used when the initial conditions are known, but the terminal condition is discovered as the block is executed. The following example defines a loop that starts with i = 0. The loop will continue to run as long as i is less than or equal to 5. i will increase by 1 each time the loop runs, as shown in Figure 7.3. Try it yourself >>

Explanation:

i is equal to 0.

While i is less than, or equal to, 5, the loop will continue to run.

i will increase by 1 each time the loop runs.

42 611944-Ch07.F.indd 42 4/20/10 1:38 PM Chapter 7: Javascript Loops Figure 7.3 The do...while Loop The do...while loop is a variant of the while loop. This loop will execute the block of code once, and then it will repeat the loop as long as the specified condition is true. The syntax is as follows: do { code to be executed } while (var<=endvalue); The following example uses a do...while loop. The do...while loop will always be executed at least once, even if the condition is false, because the statements are executed before the condition is tested. The result is shown in Figure 7.4. TIP The difference between the while and do…while loops should be characterized by whether the condition is checked before or after the block is executed. In the case of the while loop, the condition is checked first, so if false, the block will not be executed. In the do…while loop, the condition is checked after the block is executed; therefore the block is always executed at least once. 43 611944-Ch07.F.indd 43 4/20/10 1:38 PM Learn JavaScript and Ajax with w3schools Try it yourself >>

Explanation:

i equal to 0.

The loop will run

i will increase by 1 each time the loop runs.

While i is less than, or equal to, 5, the loop will continue to run.

44 611944-Ch07.F.indd 44 4/20/10 1:38 PM Chapter 7: Javascript Loops Figure 7.4 45 611944-Ch07.F.indd 45 4/20/10 1:38 PM Chapter 8 Additional JavaScript Flow Control Statements In This Chapter ❑ The break Statement ❑ The continue Statement ❑ JavaScript for...in Statement ❑ JavaScript switch Statement The break and continue statements are used to control loop execution. The break statement can be used to halt execution of a loop if, for example, an error condition is encountered. The continue statement is used to begin the next iteration of a loop without executing all the statements in the block. The break Statement The break statement will terminate execution of the loop and continue executing the code that follows after the loop (if any). Your result is shown in Figure 8.1. Try it yourself >>

Explanation: The loop will break when i=3.

Figure 8.1 The continue Statement The continue statement will terminate the current iteration and restart the loop with the next value. Your result is shown in Figure 8.2. Try it yourself >>

Explanation: The loop will break the current loop and continue with the next value when i=3.

Figure 8.2 JavaScript for...in Statement The for...in statement loops through the elements of an array or through the properties of an object. The syntax is as follows: for (variable in object) { code to be executed } NOTE The code in the body of the for...in loop is executed once for each element/property. 48 611944-Ch08.F.indd 48 4/20/10 1:38 PM Chapter 8: Additional JavaScript Flow Control Statements NOTE The variable argument can be a named variable, an array element, or a property of an object. Arrays are discussed more fully in Chapter 17, “JavaScript Array Object.” In the following example, use the for...in statement to loop through an array. Your result is shown in Figure 8.3. Try it yourself >> Figure 8.3 Conditional statements are used to perform different actions based on different conditions. 49 611944-Ch08.F.indd 49 4/20/10 1:38 PM Learn JavaScript and Ajax with w3schools JavaScript switch Statement Use the switch statement to select one of many blocks of code to be executed. The syntax is as follows: switch(n) { case 1: execute code block 1 break; case 2: execute code block 2 break; default: code to be executed if n is different from case 1 and 2 } This is how it works: First we have a single expression n (most often a variable) that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Execution continues until either the end of the switch block is reached or a break statement is encountered. For example:

Note that when i == 1 execution begins with case 1: but continues until the break statement is encountered. Your results are shown in Figure 8.4. Try it yourself >>

This JavaScript will generate a different greeting based on what day it is. Note that Sunday=0, Monday=1, Tuesday=2, etc.

(continued) 51 611944-Ch08.F.indd 51 4/20/10 1:38 PM Learn JavaScript and Ajax with w3schools (continued) Figure 8.4 52 611944-Ch08.F.indd 52 4/20/10 1:38 PM Chapter 9 JavaScript Popup Boxes In This Chapter ❑ Popup Boxes • Alert Box • Confirm Box • Prompt Box Popup Boxes JavaScript has three types of popup boxes: alert box, confirm box, and prompt box. Alert Box An alert box is often used when you want to display information to the user. When an alert box pops up, the user will have to click OK to proceed. The syntax is as follows: alert("sometext"); Your results are shown in Figure 9.1. When you click the button, the alert box in Figure 9.2 pops up. Try it yourself >> (continued) 53 611944-Ch09.F.indd 53 4/29/10 10:13 PM Learn JavaScript and Ajax with w3schools (continued) Figure 9.1 Figure 9.2 The following example creates an alert box with line breaks. Your results are shown in Figures 9.3 and 9.4. Try it yourself >> Figure 9.3 Figure 9.4 Confirm Box A confirm box is often used if you want the user to verify or accept something. When a confirm box pops up, the user will have to click either OK or Cancel to proceed. If the user clicks OK, the box returns true. If the user clicks Cancel, the box returns false. The syntax is as follows: confirm("sometext"); Your results are shown in Figures 9.5 and 9.6. Try it yourself >> Figure 9.5 Figure 9.6 Prompt Box A prompt box is often used if you want the user to input a value while on a page or from a page. When a prompt box pops up, the user will have to click either OK or Cancel to proceed after entering an input value. 56 611944-Ch09.F.indd 56 4/29/10 10:13 PM Chapter 9: JavaScript Popup Boxes If the user clicks OK, the box returns the input value. If the user clicks Cancel, the box returns null. The syntax is as follows: prompt("sometext","defaultvalue"); Your results are shown in Figure 9.7. Try it yourself >>

Figure 9.7 57 611944-Ch09.F.indd 57 4/29/10 10:13 PM Chapter 10 JavaScript Functions In This Chapter ❑ How to Define a Function ❑ JavaScript Function Examples ❑ The return Statement ❑ The Lifetime of JavaScript Variables A function will be executed by an event or by an explicit call to the function. To keep the browser from executing a script when the page loads, you can put your script into a function. A function contains code that will be executed by an event or by a call to the function. You may call a function from anywhere within a page (or even from other pages if the function is embedded in an external .js file). Functions can be defined both in the and in the section of a document. However, to ensure that a function is read/loaded by the browser before it is called, it should be placed in the section. How to Define a Function The syntax is as follows: function functionname(var1,var2,...,varX) { some code } 58 611944-Ch10.F.indd 58 4/20/10 1:39 PM Chapter 10: JavaScript Functions The parameters var1, var2, and so on, are variables or values passed into the function. The { and the } defines the start and end of the function. NOTE A function with no parameters must include the parentheses () after the function name. TIP Do not forget about the importance of capitalization in JavaScript! The word function must be written in lowercase letters, otherwise a JavaScript error occurs. Also note that you must call a function with the exact same capitalization as in the function declaration. JavaScript Function Examples In the following example, if the line alert("Hello world!!") had not been put within a function, it would have been executed as soon as the line was loaded. Now, the script will not be executed before a user clicks the input button. The function displaymessage() will be executed if the input button is clicked. Your results are shown in Figures 10.1 and 10.2. Try it yourself >>

By pressing the button above, a function will be called. The function will alert a message.

(continued) 59 611944-Ch10.F.indd 59 4/20/10 1:39 PM Learn JavaScript and Ajax with w3schools (continued) Figure 10.1 Figure 10.2 You will learn more about JavaScript events in the Chapter 11, “JavaScript Events.” The following example of a function with a parameter shows how to pass a variable to a function and use the variable in the function. Your results are shown in Figures 10.3 and 10.4. Try it yourself >>

60 611944-Ch10.F.indd 60 4/20/10 1:39 PM Chapter 10: JavaScript Functions

By pressing the button above, a function will be called with "Hello" as a parameter. The function will alert the parameter.

Figure 10.3 Figure 10.4 The following example shows how to let a function return a value. Your results are shown in Figure 10.5 Try it yourself >> (continued) 61 611944-Ch10.F.indd 61 4/20/10 1:39 PM Learn JavaScript and Ajax with w3schools (continued) Figure 10.5 The return Statement The return statement is used to specify the value that is returned from the function. So, functions that are going to return a value must use the return statement. A return statement also may be used in a function that does not return a value to end execution at any given point in the function; for example, if an error condition is encountered: Var globalName; function setGlobalName(name) { if (name.length == 0) { Alert("no name specified") return; } globalName = name; } The following example returns the product of two numbers (a and b). Your results are shown in Figure 10.6. Try it yourself >>

The script in the body section calls a function with two parameters (4 and 3).

The function will return the product of these two parameters.

Figure 10.6 The Lifetime of JavaScript Variables If you declare a variable within a function, the variable can be accessed only within that function. When you exit the function, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different functions, because each is recognized only by the function in which it is declared. If you declare a variable outside a function, all the functions on your page can access it. These variables are called global variables. The lifetime of these variables starts when they are declared and ends when the page is closed. 63 611944-Ch10.F.indd 63 4/20/10 1:39 PM Chapter 11 JavaScript Events In This Chapter ❑ onLoad and onUnload ❑ onFocus, onBlur, and onChange ❑ onSubmit ❑ onMouseOver and onMouseOut ❑ onClick Events are actions that can be detected by JavaScript. By using JavaScript, we have the ability to create dynamic Web pages. Every element on a Web page has certain events that can trigger a JavaScript. For example, we can use the onClick event of a button element to indicate that a function will run when a user clicks the button. We define the events in the HTML tags. Examples of events: 8 A mouse click 8 A Web page or an image loading 8 Mousing over a hot spot on the Web page 8 Selecting an input field in an HTML form 8 Submitting an HTML form N O TE Events are normally used in combination with functions, and the function will not be executed before the event occurs! onLoad and onUnload The onLoad and onUnload events are triggered when the user enters or leaves the page. The onLoad event is often used to check the visitor’s browser type and browser version and load the proper version of the Web page based on the information. 64 611944-Ch11.F.indd 64 4/20/10 1:39 PM Chapter 11: JavaScript Events Both the onLoad and onUnload events often are used to deal with cookies that should be set when a user enters or leaves a page. For example, you could have a popup asking for the user’s name upon his first arrival to your page. The name is then stored in a cookie. Next time the visitor arrives at your page, you could have another popup saying something like: “Welcome John Doe!”. onFocus, onBlur, and onChange The onFocus, onBlur, and onChange events are often used in combination with validation of form fields. The onFocus and onBlur events are complementary and are caused by the user clicking outside of the current window, frame, or form element or using the Tab key to move among fields or elements. When the user leaves an element, that element triggers a blur event. When the user moves to a new element, that element triggers a focus event. Following is an example of how to use the onChange event. The checkEmail() function will be called whenever the user changes the content of the field: onSubmit The onSubmit event may be used to validate form fields before submitting the form. TIP Because the programmer controls the function executed on onSubmit, he can validate any, all, or no inputs as he sees fit. Following is an example of how to use the onSubmit event. The checkForm() function will be called when the user clicks the Submit button in the form. If the field values are not accepted, the submit should be cancelled. The function checkForm() returns either true or false. If it returns true, the form will be submitted, otherwise the submit will be cancelled:

65 611944-Ch11.F.indd 65 4/20/10 1:39 PM Learn JavaScript and Ajax with w3schools onMouseOver and onMouseOut onMouseOver and onMouseOut often are used to create Rollover buttons. Following is an example of an onMouseOver event. An alert box appears when an onMouseOver event is detected: onClick The onClick event occurs when the user mouse clicks on a visible element on the screen. The following example could be used to translate text on a page when requested by the user: 66 611944-Ch11.F.indd 66 4/20/10 1:39 PM Chapter 12 javascript try…catch and Throw Statements In This Chapter ❑ JavaScript—Catching Errors ❑ The try...catch Statement ❑ The throw Statement The try…catch statement enables you to trap errors that occur during the execution of a block of code. JavaScript—Catching Errors When browsing Web pages on the Internet, we all have seen a JavaScript alert box telling us there is a runtime error and asking “Do you wish to debug?” Error messages like this may be useful for developers but not for users. When users see errors, they often leave the Web page. This chapter teaches you how to catch and handle JavaScript error messages so you don’t lose your audience. The try...catch Statement The try…catch statement enables you to trap errors that occur during the execution of a block of code. The try block contains the code to be run, and the catch block contains the code to be executed if an error occurs. 67 611944-Ch12.F.indd 67 4/20/10 1:40 PM Learn JavaScript and Ajax with w3schools The syntax is as follows: try { //Run some code here } catch(err) { //Handle errors here } NOTE Note that try...catch is written in lowercase letters. Using uppercase letters will generate a JavaScript error! The following example is supposed to alert “Welcome guest!” when the button is clicked. However, there’s a typo in the message() function. alert() is misspelled as adddlert(). A JavaScript error occurs. The catch block catches the error and executes a custom code to handle it. The code displays a custom error message informing the user what happened. Your results are shown in Figures 12.1 and 12.2. Try it yourself >> 68 611944-Ch12.F.indd 68 4/20/10 1:40 PM Chapter 12: JavaScript Try…Catch and Throw Statements Figure 12.1 Figure 12.2 The next example uses a confirm box to display a custom message telling users they can click OK to continue viewing the page or click Cancel to go to the homepage. If the confirm method returns false, the user clicked Cancel, and the code redirects the user. If the confirm method returns true, the code does nothing. Your results are shown in Figures 12.3 and 12.4. Try it yourself >> Figure 12.3 Figure 12.4 The throw Statement The throw statement allows you to create an exception. If you use this statement together with the try...catch statement, you can control program flow and generate accurate error messages. 70 611944-Ch12.F.indd 70 4/20/10 1:40 PM Chapter 12: JavaScript Try…Catch and Throw Statements The syntax is as follows: throw(exception) The exception can be a string, integer, Boolean, or an object. NOTE throw is written in lowercase letters. Using uppercase letters will generate a JavaScript error! The following example determines the value of a variable called x. If the value of x is higher than 10, lower than 0, or not a number, we are going to throw an error. The error is then caught by the catch argument, and the proper error message is displayed: 72 611944-Ch12.F.indd 72 4/20/10 1:40 PM Chapter 13 JavaScript Special Characters and Guidelines In This Chapter ❑ Insert Special Characters ❑ JavaScript Is Case Sensitive ❑ White Space ❑ Break up a Code Line In JavaScript, you can add special characters to a text string by using the backslash character. Also, when scripting with JavaScript, you should know some other important guidelines. Insert Special Characters The backslash (\) is used to insert apostrophes, new lines, quotes, and other special characters into a text string. Look at the following JavaScript code: var txt="We are the so-called "Vikings" from the north."; document.write(txt); In JavaScript, a string is started and stopped with either single or double quotes. This means that the preceding string will be chopped to We are the so-called. To solve this problem, you must place a backslash (\) before each double quote in “Viking”. This turns each double quote into a string literal: var txt="We are the so-called \"Vikings\" from the north."; document.write(txt); 73 611944-Ch13.F.indd 73 4/20/10 1:40 PM Learn JavaScript and Ajax with w3schools JavaScript will now output the proper text string: We are the so-called “Vikings” from the north. Here is another example: document.write ("You \& I are singing!"); The previous example will produce the following output: You & I are singing! The following table lists other special characters that can be added to a text string with the backslash sign: Code \’ \” \& \\ \n \r \t \b \f Outputs single quote double quote ampersand backslash new line carriage return tab backspace form feed JavaScript Is Case Sensitive A function named myfunction is not the same as myFunction and a variable named myVar is not the same as myvar. JavaScript is case sensitive; therefore, watch your capitalization closely when you create or call variables, objects, and functions. White Space JavaScript ignores extra spaces. You can add white space to your script to make it more readable. The following lines are equivalent: name="Hege"; name = "Hege"; Break up a Code Line Text in code statements contained within quotes is called a string literal. A string literal may not be broken across lines except by inserting the backslash character (\) at the point where you want to break the string: document.write("Hello \ World!"); 74 611944-Ch13.F.indd 74 4/20/10 1:40 PM Chapter 13: JavaScript Special Characters and Guidelines The following will generate an “unterminated string literal” script error: document.write("Hello World!"); Another option is to use the concatenate operator (+) to break the string: document.write("Hello "+ "World!"); Code statements may be broken across lines, but the backslash character must not be used in this case. The following is legal JavaScript: document.write ("Hello " + World!" ); As a rule, break code statements or string literals across lines only when the length of the line or literal makes it difficult to read. You can break up a code line within a text string with a backslash. The following example will be displayed properly: document.write("Hello \ World!"); However, you cannot break up a code line like this: document.write \ ("Hello World!"); 75 611944-Ch13.F.indd 75 4/20/10 1:40 PM 611944-Ch13.F.indd 76 4/20/10 1:40 PM Section II JavaScript Objects ❑ Chapter 14: JavaScript Objects Intro ❑ Chapter 15: JavaScript String Object ❑ Chapter 16: JavaScript Date Object ❑ Chapter 17: JavaScript Array Object ❑ Chapter 18: JavaScript Boolean Object ❑ Chapter 19: JavaScript Math Object ❑ Chapter 20: JavaScript RegExp Objects 77 611944-Ch14.F.indd 77 4/20/10 1:41 PM 611944-Ch14.F.indd 78 4/20/10 1:41 PM Chapter 14 JavaScript Objects Intro In This Chapter ❑ Object-Oriented Programming ❑ Properties ❑ Methods JavaScript as a programming language has strong object-oriented capabilities. An Object-Oriented (OOL) language enables you to model data using objects consisting of properties and methods that operate on those properties. Object-Oriented Programming Creating your own objects is explained later in the section “Advanced JavaScript.” We start by looking at the built-in JavaScript objects and how they are used. The next pages explain each built-in JavaScript object in detail. Note that an object is just a special kind of data. An object has properties and methods. Properties Properties are the values associated with an object. In the following example, we use the length property of the String object to return the number of characters in a string: (continued) 79 611944-Ch14.F.indd 79 4/20/10 1:41 PM Learn JavaScript and Ajax with w3schools (continued) The output of the previous code will be 12 Methods Methods are the actions that can be performed on objects. In the following example, we use the toUpperCase() method of the String object to display a text in uppercase letters: The output of the previous code will be HELLO WORLD! 80 611944-Ch14.F.indd 80 4/20/10 1:41 PM Chapter 15 JavaScript String Object In This Chapter ❑ String Object ❑ Examples The String object is used to manipulate a stored piece of text. String Object The following example uses the length property of the String object to find the length of a string: var txt="Hello world!"; document.write(txt.length); The preceding code will result in the following output: 12 The following example uses the toUpperCase() method of the String object to convert a string to uppercase letters: var txt="Hello world!"; document.write(txt.toUpperCase()); The preceding code will result in the following output: HELLO WORLD! 81 611944-Ch15.F.indd 81 4/20/10 1:42 PM Learn JavaScript and Ajax with w3schools Examples The following example shows how to return the length of a string. Your results are shown in Figure 15.1. Try it yourself >> Figure 15.1 The following example demonstrates how to use the methods of the String object to style strings. Your results are shown in Figure 15.2. Try it yourself >> 83 611944-Ch15.F.indd 83 4/20/10 1:42 PM Learn JavaScript and Ajax with w3schools Figure 15.2 The following example demonstrates conversion of a string to lowercase or uppercase. Your results are shown in Figure 15.3. Try it yourself >> 84 611944-Ch15.F.indd 84 4/20/10 1:42 PM Chapter 15: JavaScript String Object Your results are shown in Figure 15.3. Figure 15.3 The following example demonstrates how to search for a specified value within a string. Your results are shown in Figure 15.4. Try it yourself >> Figure 15.4 The following example shows how to replace a specified value with another value in a string. Your results are shown in Figure 15.5. 85 611944-Ch15.F.indd 85 4/20/10 1:42 PM Learn JavaScript and Ajax with w3schools Try it yourself >> Figure 15.5 The following example demonstrates how to find the position of the first occurrence of a specified value in a string. Your results are shown in Figure 15.6. Try it yourself >> 86 611944-Ch15.F.indd 86 4/20/10 1:42 PM Chapter 15: JavaScript String Object Figure 15.6 For  a complete reference of all the properties and methods that can be used with the String object, go to the String object reference in Appendix A. The reference contains a brief description and usage examples for each property and method! 87 611944-Ch15.F.indd 87 4/20/10 1:42 PM Chapter 16 JavaScript Date Object In This Chapter ❑ Create a Date Object ❑ Set Dates ❑ Compare Two Dates ❑ Examples The Date object is used to work with dates and times. Create a Date Object The Date object is used to work with dates and times. Date objects are created with the Date() constructor. There are four ways of instantiating a date: new Date() // current date and time new Date(milliseconds) //milliseconds since 1970/01/01 new Date(dateString) new Date(year, month, day, hours, minutes, seconds, milliseconds) Most of the preceding parameters are optional. When a parameter is not specified, 0 is passed to the method by default. After a Date object is created, a number of methods enable you to operate on it. Most methods allow you to get and set the year, month, day, hour, minute, second, and millisecond of the object, using either local time or UTC (universal, or GMT) time. 88 611944-Ch16.F.indd 88 4/20/10 1:43 PM Chapter 16: JavaScript Date Object All dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC) with a day containing 86,400,000 milliseconds. Some examples of instantiating a date: today = new Date() d1 = new Date(“October 13, 1975 11:13:00”) d2 = new Date(79,5,24) d3 = new Date(79,5,24,11,33,0) For a complete reference of all the properties and methods that can be used with the Date object, go to the complete Date object reference in Appendix A. The reference contains a brief description and examples of use for each property and method! Set Dates We can easily manipulate the date by using the methods available for the Date object. In the following example, we set a Date object to a specific date (14th January 2010): var myDate=new Date(); myDate.setFullYear(2010,0,14); And in the following example, we set a Date object to be five days into the future: var myDate=new Date(); myDate.setDate(myDate.getDate()+5); N O TE If adding five days to a date shifts the month or year, the changes are handled automatically by the Date object itself! Compare Two Dates The Date object is also used to compare two dates. The following example compares today’s date with the 14th January 2010: var myDate=new Date(); myDate.setFullYear(2010,0,14); var today = new Date(); if (myDate>today) { (continued) 89 611944-Ch16.F.indd 89 4/20/10 1:43 PM Learn JavaScript and Ajax with w3schools (continued) alert(“Today is before 14th January 2010”); } else { alert(“Today is after 14th January 2010”); } Examples The following example demonstrates how to use the Date() method to get today’s date. Your results are shown in Figure 16.1. Try it yourself >> Figure 16.1 The following example demonstrates how to use getTime() to calculate the milliseconds since 1970. Your results are shown in Figure 16.2. Try it yourself >> 90 611944-Ch16.F.indd 90 4/20/10 1:43 PM Chapter 16: JavaScript Date Object Figure 16.2 The following example shows how to use setFullYear() to set a specific date. Your results are shown in Figure 16.3. Try it yourself >> Figure 16.3 The following example demonstrates how to use toUTCString() to convert today’s date (according to UTC) to a string. Your results are shown in Figure 16.4. 91 611944-Ch16.F.indd 91 4/20/10 1:43 PM Learn JavaScript and Ajax with w3schools Try it yourself >> Figure 16.4 The getDay() method returns the day of the week as a number, with Sunday = 0. The following example demonstrates how to use getDay() and an array to display the day of the week as a text string rather than a number as shown in Figure 16.5. Try it yourself >> Figure 16.5 The following example demonstrates how to display a clock on your Web page. Your results are shown in Figure 16.6. Try it yourself >>

Figure 16.6 94 611944-Ch16.F.indd 94 4/20/10 1:43 PM Chapter 17 JavaScript Array Object In This Chapter ❑ What Is an Array? ❑ Create an Array ❑ Access an Array ❑ Modify Values in an Array ❑ Examples The Array object is used to store multiple values in a single variable. What Is an Array? An array is a special variable that can hold more than one value at a time. If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this: cars1="Saab"; cars2="Volvo"; cars3="BMW"; However, what if you want to loop through the cars and find a specific one? And what if you had not three cars, but 300? The best solution here is to use an array. An array can hold all your variable values under a single name. And you can access the values by referring to the array name. Each element in the array has its own ID so that it can be easily accessed. 95 611944-Ch17.F.indd 95 4/20/10 1:43 PM Learn JavaScript and Ajax with w3schools Create an Array An array can be defined in three ways. The following code creates an Array object called myCars: 1. var myCars=new Array(); // create a new array with no elements // new Array(n); will create a new array of length n myCars[0]="Saab"; myCars[1]="Volvo"; myCars[2]="BMW"; 2. var myCars=new Array("Saab","Volvo","BMW"); // create a new array with the specified elements 3. var myCars=["Saab","Volvo","BMW"]; //examples 2 & 3 are functionally equivalent N O TE If you specify numbers or true/false values inside the array then the variable type will be Number or Boolean, instead of String. Access an Array You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0. The following code line document.write(myCars[0]); results in the following output: Saab Modify Values in an Array To modify a value in an existing array, just specify a new value for the element at the given index. myCars[0]="Opel"; myCars[0] // overwrite the current value of 96 611944-Ch17.F.indd 96 4/20/10 1:43 PM Chapter 17: JavaScript Array Object Now, the following code line: document.write(myCars[0]); results in the following output: Opel Examples The following example demonstrates how to create an array, assign values to it, and write the values to the output. Your results are shown in Figure 17.1. Try it yourself >> Figure 17.1 97 611944-Ch17.F.indd 97 4/20/10 1:43 PM Learn JavaScript and Ajax with w3schools The following example demonstrates how to use a for...in statement to loop through the elements of an array. Your results are shown in Figure 17.2. Try it yourself >> Figure 17.2 The following example demonstrates how to join two arrays. Your results are shown in Figure 17.3 Figure 17.3 The following example demonstrates how to join three arrays. Your results are shown in Figure 17.4 Figure 17.4 The following example shows you how to join all elements of an array into a string. Your results are shown in Figure 17.5. Figure 17.5 The following example demonstrates how to remove the last element of an array, and Figure 17.6 shows your results. Figure 17.6 The following example demonstrates how to add new elements to the end of an array. Your results are shown in Figure 17.7. 100 611944-Ch17.F.indd 100 4/20/10 1:43 PM Chapter 17: JavaScript Array Object Figure 17.7 In the following example, you see how to reverse the order of the elements in an array. Your results are shown in Figure 17.8. Figure 17.8 The following example demonstrates how to remove the first element of an array. Your results are shown in Figure 17.9. Figure 17.9 The following example demonstrates how to use slice() to select elements from an array. Your results are shown in Figure 17.10. Figure 17.10 102 611944-Ch17.F.indd 102 4/20/10 1:43 PM Chapter 17: JavaScript Array Object The following three examples demonstrate how to use sort(). The first sort() example shows how to sort alphabetically and ascending. Your results are shown in Figure 17.11. Figure 17.11 The next sort() example demonstrates how to sort numerically and ascending. Your results are shown in Figure 17.12. Figure 17.12 103 611944-Ch17.F.indd 103 4/20/10 1:43 PM Learn JavaScript and Ajax with w3schools The third sort() example demonstrates how to sort numerically and descending. Your results are shown in Figure 17.13. Figure 17.13 The following example demonstrates how to use splice() to add an element to the second position in an array. Your results are shown in Figure 17.14. 104 611944-Ch17.F.indd 104 4/20/10 1:43 PM Chapter 17: JavaScript Array Object Figure 17.14 The following example shows you how to convert an array to a string. Your results are shown in Figure 17.15. Figure 17.15 The following example shows you how to add new elements to the beginning of an array. Figure 17.16 shows your results.

Note: The unshift() method does not work properly in Internet Explorer, it only returns undefined!

(continued) 105 611944-Ch17.F.indd 105 4/20/10 1:43 PM Learn JavaScript and Ajax with w3schools (continued) Figure 17.16 N O TE The unshift() method does not work properly in Internet Explorer, it only returns undefined, as shown in Figure 17.17. Figure 17.17 You can follow these examples on the w3Schools Web site. For a complete reference of all the properties and methods that can be used with the Array object, go to the complete Array object reference in Appendix A. 106 611944-Ch17.F.indd 106 4/20/10 1:43 PM Chapter 18 JavaScript Boolean Object In This Chapter ❑ Create a Boolean Object ❑ Examples The Boolean object is used to convert a non-Boolean value to a Boolean value (either true or false). Create a Boolean Object The Boolean object represents two values: true or false. The following code creates a Boolean object called myBoolean: var myBoolean=new Boolean(); NOTE If the Boolean object has no initial value or if it is 0, -0, null, “”, false, undefined, or NaN, the object is set to false. Otherwise, it is true (even with the string “false”)! All the following lines of code create Boolean objects with an initial value of false: var myBoolean=new Boolean(); var myBoolean=new Boolean(0); var myBoolean=new Boolean(null); var myBoolean=new Boolean(""); var myBoolean=new Boolean(false); var myBoolean=new Boolean(NaN); 107 611944-Ch18.F.indd 107 4/20/10 1:44 PM Learn JavaScript and Ajax with w3schools And all the following lines of code create Boolean objects with an initial value of true: var myBoolean=new Boolean(true); var myBoolean=new Boolean("true"); var myBoolean=new Boolean("false"); var myBoolean=new Boolean("Richard"); For a complete reference of all the properties and methods that can be used with the Boolean object, go to the complete Boolean object reference in Appendix A. Examples The following example demonstrates how to check whether a Boolean object is true or false. Your result is shown in Figure 18.1. Try it yourself >> 108 611944-Ch18.F.indd 108 4/20/10 1:44 PM Chapter 18: JavaScript Boolean Object Figure 18.1 109 611944-Ch18.F.indd 109 4/20/10 1:44 PM Chapter 19 JavaScript Math Object In This Chapter ❑ Math Object ❑ Mathematical Constants ❑ Mathematical Methods ❑ Examples The Math object allows you to perform mathematical tasks. Math Object The Math object allows you to perform mathematical tasks. The Math object includes several mathematical constants and methods. The syntax for using properties/methods of Math is as follows: var pi_value=Math.PI; var sqrt_value=Math.sqrt(16); N O TE The Math object is provided by JavaScript and does not need to be created by the programmer. In fact, trying to create a Math object using new() will result in a JavaScript error. Mathematical Constants JavaScript provides eight mathematical constants that can be accessed from the Math object. These are E, PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log of E. You may reference these constants from your JavaScript like this: 110 611944-Ch19.F.indd 110 4/20/10 1:44 PM Chapter 19: JavaScript Math Object Math.E Math.PI Math.SQRT2 Math.SQRT1_2 Math.LN2 Math.LN10 Math.LOG2E Math.LOG10E Mathematical Methods In addition to the mathematical constants that can be accessed from the Math object, several methods also are available. The following example uses the round() method of the Math object to round a number to the nearest integer: document.write(Math.round(4.7)); The preceding code results in the following output: 5 The following example uses the random() method of the Math object to return a random number between 0 and 1: document.write(Math.random()); The preceding code can result in the following output: 0.07730209357983464 The following example uses the floor() and random() methods of the Math object to return a random number between 0 and 10: document.write(Math.floor(Math.random()*11)); The preceding code can result in the following output: 1 For a complete reference of all the properties and methods that can be used with the Math object, go to the complete Math object reference in Appendix A. 111 611944-Ch19.F.indd 111 4/20/10 1:44 PM Learn JavaScript and Ajax with w3schools Examples The following example demonstrates how to use round(). Your results are shown in Figure 19.1. Try it yourself >> Figure 19.1 The following example demonstrates how to use random() to return a random number between 0 and 1 as shown in Figure 19.2. Try it yourself >> Figure 19.2 The following example demonstrates how to use max() to return the largest of the specified values. Your results are shown in Figure 19.3. Try it yourself >> Figure 19.3 113 611944-Ch19.F.indd 113 4/20/10 1:44 PM Learn JavaScript and Ajax with w3schools The following example shows how to use min() to return the smallest of the specified values. Your results are shown in Figure 19.4. Try it yourself >> Figure 19.4 114 611944-Ch19.F.indd 114 4/20/10 1:44 PM Chapter 20 JavaScript RegExp Object In This Chapter ❑ What Is RegExp? ❑ RegExp Modifiers ❑ test() ❑ exec() RegExp is short for regular expression. What Is RegExp? A regular expression is an object that describes a pattern of characters. When you search in a text, you can use a pattern to describe what you are searching for. A simple pattern can be a single character. A more complicated pattern can consist of more characters and can be used for parsing, format checking, substitution, and more. Regular expressions are used to perform powerful pattern-matching and searchand-replace functions on text. The syntax is as follows: var txt=new RegExp(pattern,modifiers); or more simply: var txt=/pattern/modifiers; 115 611944-Ch20.F.indd 115 4/20/10 1:44 PM Learn JavaScript and Ajax with w3schools The syntax follows a couple of general guidelines: 8 The pattern specifies the pattern of an expression. 8 The modifiers specify whether a search should be global, case-sensitive, and so on. RegExp Modifiers Modifiers are used to perform case-insensitive and global searches. The i modifier is used to perform case-insensitive matching. The g modifier is used to perform a global match (find all matches rather than stopping after the first match). The following example demonstrates how to do a case-insensitive search for “w3schools” in a string: var str="Visit W3Schools"; var patt1=/w3schools/i; Your results are shown in Figure 20.1. Try it yourself >> Figure 20.1 116 611944-Ch20.F.indd 116 4/20/10 1:44 PM Chapter 20: JavaScript RegExp Object The following example demonstrates how to do a global search for “is”: var str="Is this all there is?"; var patt1=/is/g; Your results are shown in Figure 20.2. Try it yourself >> Figure 20.2 The following example demonstrates how to do a global, case-insensitive search for “is”: var str="Is this all there is?"; var patt1=/is/gi; Your results are shown in Figure 20.3. Try it yourself >> (continued) 117 611944-Ch20.F.indd 117 4/20/10 1:44 PM Learn JavaScript and Ajax with w3schools (continued) Figure 20.3 test() The test() method searches a string for a specified value and returns true or false, depending on the result. The following example searches a string for the character “e”: var patt1=new RegExp("e"); document.write(patt1.test("The best things in life are free")); Because there is an “e” in the string, the output of the preceding code is as follows: true Your results are shown in Figure 20.4. Try it yourself >> Figure 20.4 exec() The exec() method searches a string for a specified value and returns the text of the found value. If no match is found, it returns null. The following example searches a string for the character “e”: var patt1=new RegExp("e"); document.write(patt1.exec("The best things in life are free")); Because there is an “e” in the string, the output of the preceding code is: e Your results are shown in Figure 20.5. Try it yourself >> 119 611944-Ch20.F.indd 119 4/20/10 1:44 PM Learn JavaScript and Ajax with w3schools Figure 20.5 For a complete reference of all the properties and methods that can be used with the RegExp object, go to the complete RegExp object reference in Appendix A. 120 611944-Ch20.F.indd 120 4/20/10 1:44 PM Section III JavaScript Advanced ❑ Chapter 21: JavaScript Browser Detection ❑ Chapter 22: JavaScript Cookies ❑ Chapter 23: JavaScript Form Validation ❑ Chapter 24: JavaScript Animation ❑ Chapter 25: JavaScript Image Maps ❑ Chapter 26: JavaScript Timing Events ❑ Chapter 27: Create Your Own Objects with JavaScript 121 611944-Ch21.F.indd 121 4/20/10 1:45 PM 611944-Ch21.F.indd 122 4/20/10 1:45 PM Chapter 21 JavaScript Browser Detection In This Chapter ❑ Browser Detection ❑ The Navigator Object The Navigator object contains information about the visitor’s browser. Browser Detection Almost everything in this tutorial works on all JavaScript-enabled browsers. However, some things just don’t work on certain browsers—especially on older browsers. So, sometimes it can be very useful to detect the visitor’s browser and then serve up the appropriate information. The best way to do this is to make your Web pages smart enough to look one way to some browsers and another way to other browsers. The Navigator object can be used for this purpose. The Navigator object contains information about the visitor’s browser name, version, and more. NOTE No public standard applies to the Navigator object, but all major browsers support it. 123 611944-Ch21.F.indd 123 4/20/10 1:45 PM Learn JavaScript and Ajax with w3schools The Navigator Object The Navigator object contains all information about the visitor’s browser. We are going to look at two properties of the Navigator object: 8 appName—holds the name of the browser 8 appVersion—holds, among other things, the version of the browser Your results are shown in Figure 21.1. Try it yourself >> Figure 21.1 The variable “browser” in the preceding example holds the name of the browser, that is, “Netscape” or “Microsoft Internet Explorer.” The appVersion property in the preceding example returns a string that contains much more information than just the version number, but for now we are only interested in the version number. To pull the version number out of the string, we are using a function called parseFloat(), which pulls the first thing that looks like a decimal number out of a string and returns it. TIP To find the version number in IE 5.0 and later, you will have to dig a little deeper into either the appVersion or userAgent property. The IE version will be in the form “MSIE x.x” so use a regular expression such as /MSIE \d\.\d;/.exec(navigator. userAgent)to return a string containing the specific IE version. 124 611944-Ch21.F.indd 124 4/20/10 1:45 PM Chapter 21: JavaScript Browser Detection The following example displays a different alert, depending on the visitor’s browser. The alert box is shown in Figure 21.2. Try it yourself >> Figure 21.2 125 611944-Ch21.F.indd 125 4/20/10 1:45 PM Learn JavaScript and Ajax with w3schools The following example provides more rules about the visitor’s browser. Your results are shown in Figure 21.3. Try it yourself >> Figure 21.3 126 611944-Ch21.F.indd 126 4/20/10 1:45 PM Chapter 21: JavaScript Browser Detection The following example provides ALL the details about the visitor’s browser. Your results are shown in Figure 21.4. Try it yourself >> 127 611944-Ch21.F.indd 127 4/20/10 1:45 PM Learn JavaScript and Ajax with w3schools Figure 21.4 128 611944-Ch21.F.indd 128 4/20/10 1:45 PM Chapter 22 JavaScript Cookies In This Chapter ❑ What Is a Cookie? ❑ Create and Store a Cookie A cookie is often used to identify a user. What Is a Cookie? A cookie is a variable that is stored on the visitor’s computer. Each time the same computer requests a page with a browser, it sends the cookie, too. With JavaScript, you can both create and retrieve cookie values. Examples of cookies: 8 Name cookie. The first time a visitor arrives on your Web page, she must fill in her name. The name then is stored in a cookie. Next time the visitor arrives at your page, she could get a welcome message like “Welcome Jane Doe!” The name is retrieved from the stored cookie. 8 Password cookie. The first time a visitor arrives on your Web page, she must fill in a password. The password then is stored in a cookie. Next time the visitor arrives at your page, the password is retrieved from the cookie. 8 Date cookie. The first time a visitor arrives to your Web page, the current date is stored in a cookie. Next time the visitor arrives at your page, she could get a message like “Your last visit was on Tuesday, August 11, 2005!” The date is retrieved from the stored cookie. 129 611944-Ch22.F.indd 129 4/20/10 1:45 PM Learn JavaScript and Ajax with w3schools Create and Store a Cookie In this example we create a cookie that stores the name of a visitor. The first time a visitor arrives at the Web page, she is asked to fill in her name. The name then is stored in a cookie. The next time the visitor arrives at the same page, she sees a welcome message. First, we create a function that stores the name of the visitor in a cookie variable: function setCookie(c_name,value,expiredays) { var exdate=new Date(); exdate.setDate(exdate.getDate()+expiredays); document.cookie=c_name+ "=" +escape(value)+ ((expiredays==null) ? "" : ";expires="+exdate.toGMTString()); } The parameters of the preceding function hold the name of the cookie, the value of the cookie, and the number of days until the cookie expires. In the preceding function, we first convert the number of days to a valid date and then we add the number of days until the cookie should expire. After that, we store the cookie name, cookie value, and the expiration date in the document.cookie object. Then we create another function that checks whether the cookie has been set: function getCookie(c_name) { if (document.cookie.length>0) { c_start=document.cookie.indexOf(c_name + "="); if (c_start!=-1) { c_start=c_start + c_name.length+1; c_end=document.cookie.indexOf(";",c_start); if (c_end==-1) c_end=document.cookie.length; return unescape(document.cookie.substring(c_start,c_ end)); } } return ""; } 130 611944-Ch22.F.indd 130 4/20/10 1:45 PM Chapter 22: JavaScript Cookies The preceding function first checks whether a cookie is stored at all in the document.cookie object. If the document.cookie object holds some cookies, then check to see whether our specific cookie is stored. If our cookie is found, then return the value; if not, return an empty string. Last, we create the function that displays a welcome message if the cookie is set, and if the cookie is not set, it displays a prompt box asking for the name of the user: function checkCookie() { username=getCookie('username'); if (username!=null && username!="") { alert('Welcome again '+username+'!'); } else { username=prompt('Please enter your name:',""); if (username!=null && username!="") { setCookie('username',username,365); } } } The following example runs the checkCookie() function when the page loads. The resulting dialog box is shown in Figure 22.1. Try it yourself >> 132 611944-Ch22.F.indd 132 4/20/10 1:45 PM Chapter 22: JavaScript Cookies Figure 22.1 133 611944-Ch22.F.indd 133 4/20/10 1:45 PM Chapter 23 JavaScript Form Validation In This Chapter ❑ Required Fields ❑ E-mail Validation JavaScript can be used to validate data in HTML forms before sending off the content to a server. Form data that typically are checked by a JavaScript could be: 8 Has the user left required fields empty? 8 Has the user entered a valid e-mail address? 8 Has the user entered a valid date? 8 Has the user entered text in a numeric field? Required Fields The following function checks whether a required field has been left empty. If the required field is blank, an alert is displayed, and the function returns false. If a value is entered, the function returns true (means that data is OK): function validate_required(field,alerttxt) { with (field) { if (value==null||value==””) { alert(alerttxt);return false; } else 134 611944-Ch23.F.indd 134 4/20/10 1:45 PM Chapter 23: JavaScript Form Validation { return true; } } } The entire script with the HTML form could look something like this: (continued) 135 611944-Ch23.F.indd 135 4/20/10 1:45 PM Learn JavaScript and Ajax with w3schools (continued) Email:

E-mail Validation The following function checks whether the content follows the general syntax of an e-mail address. NOTE This function only checks that the content appears to be an e-mail with the proper format. It does not verify that the e-mail address actually exists. This means that the input data must contain at least an @ sign and a dot (.). Also, the @ must not be the first character of the e-mail address, and the last dot must at least be one character after the @ sign: function validate_email(field,alerttxt) { with (field) { apos=value.indexOf(“@”); dotpos=value.lastIndexOf(“.”); if (apos<1||dotpos-apos<2) {alert(alerttxt);return false;} else {return true;} } } The entire script with the HTML form could look something like this:

Email:

137 611944-Ch23.F.indd 137 4/20/10 1:45 PM Chapter 24 JavaScript Animation In This Chapter ❑ The HTML Code ❑ The JavaScript Code ❑ The Entire Code With JavaScript, we can create animated images. The trick is to let a JavaScript change between different images on different events. In the following example, we add an image that should act as a link button on a Web page. We then add an onMouseOver event and an onMouseOut event that will run two JavaScript functions that change between the images. The HTML Code The HTML code looks like this: Note that we have given the image an id, to make it possible for JavaScript to address it later. The onMouseOver event tells the browser that once a mouse is rolled over the image, the browser should execute a function that replaces the image with another image. The onMouseOut event tells the browser that once a mouse is rolled away from the image, another JavaScript function should be executed. This function inserts the original image again. 138 611944-Ch24.F.indd 138 4/20/10 1:46 PM Chapter24: JavaScript Animation The JavaScript Code The changing between the images is done with the following JavaScript: The function mouseOver() causes the image to shift to “b_blue.gif.” The function mouseOut() causes the image to shift to “b_pink.gif.” The Entire Code In the following example, we combine the HTML and JavaScript code to produce animation. The resulting animation is shown in Figure 24.1. You can try this example on the www.w3schools.com Web site or include you own graphic files in the directory with your html source, substituting for b_blue and b_pink in the html source code. Try it yourself >> Figure 24.1 140 611944-Ch24.F.indd 140 4/20/10 1:46 PM Chapter 25 JavaScript Image Maps In This Chapter ❑ HTML Image Maps ❑ Adding Some JavaScript An image map is an image with clickable regions. HTML Image Maps If you’ve read Learn HTML and CSS with w3schools or completed the HTML tutorial on the w3schools Web site, you know that an image map is an image with clickable regions. Normally, each region has an associated hyperlink. Clicking on one of the regions takes you to the associated link. Look at the simple HTML image map. The result of an image map is shown in Figure 25.1. Try it yourself >> Figure 25.1 Adding Some JavaScript We can add events (that can call a JavaScript) to the tags inside the image map. The tag supports the onClick, onDblClick, onMouseDown, onMouseUp, onMouseOver, onMouseMove, onMouseOut, onKeyPress, onKeyDown, onKeyUp, onFocus, and onBlur events. Here’s the HTML image-map example, with some JavaScript added. Your results are shown in Figure 25.2. Try it yourself >> 142 611944-Ch25.F.indd 142 4/20/10 1:47 PM Chapter 25: JavaScript Image Maps

Figure 25.2 143 611944-Ch25.F.indd 143 4/20/10 1:47 PM Chapter 26 JavaScript Timing Events In This Chapter ❑ The setTimeout() Method ❑ The clearTimeout() Method With JavaScript, it is possible to execute some code after a specified time interval. This is called timing events. It’s very easy to time events in JavaScript. The two key methods that are used are as follows: 8 setTimeout()—Executes a code some time in the future 8 clearTimeout()—Cancels the setTimeout() N O TE The setTimeout() and clearTimeout() are both methods of the HTML DOM Window object. The setTimeout() Method The syntax is as follows: var t=setTimeout("javascript statement",milliseconds); The setTimeout() method returns a value. In the preceding statement, the value is stored in a variable called t. If you want to cancel this setTimeout(), you can refer to it using the variable name. The first parameter of setTimeout() is a string that contains a JavaScript statement. This statement could be a statement like "alert('5 seconds!')" or a call to a function, like "alertMsg()". The second parameter indicates how many milliseconds from now you want to execute the first parameter. 144 611944-Ch26.F.indd 144 4/20/10 1:47 PM Chapter 26: JavaScript Timing Events N O TE There are 1000 milliseconds in 1 second. When the button is clicked in the following example, an alert box is displayed after 3 seconds. Your results are shown in Figure 26.1. Try it yourself >>

Figure 26.1 To get a timer to work in an infinite loop, you must write a function that calls itself. In the following example, when a button is clicked, the input field starts to count (forever) starting at 0. Notice that you also have a function that checks whether the timer is already running, to avoid creating additional timers if the button is clicked more than once. Your results are shown in Figure 26.2. 145 611944-Ch26.F.indd 145 4/20/10 1:47 PM Learn JavaScript and Ajax with w3schools Try it yourself >>

Click on the button above. The input field will count forever, starting at 0.

146 611944-Ch26.F.indd 146 4/20/10 1:47 PM Chapter 26: JavaScript Timing Events Figure 26.2 The following example is another simple timing using the setTimeout() method. Your results are shown in Figure 26.3. Try it yourself >>

Click on the button above. The input field will tell you when two, four, and six seconds have passed.

147 611944-Ch26.F.indd 147 4/20/10 1:47 PM Learn JavaScript and Ajax with w3schools Figure 26.3 The following example shows a clock created with a timing event. Your results are shown in Figure 26.4. Try it yourself >> 148 611944-Ch26.F.indd 148 4/20/10 1:48 PM Chapter 26: JavaScript Timing Events Figure 26.4 The clearTimeout() Method The syntax is as follows: clearTimeout(setTimeout_variable) The following example is the same as the previous infinite loop example. The only difference is that we have now added a "Stop Count!" button that stops the timer. Your results are shown in Figure 26.5. Try it yourself >>

Click The the the on the "Start count!" button above to start the timer. input field will count forever, starting at 0. Click on "Stop count!" button to stop the counting. Click on "Start count!" button to start the timer again.

Figure 26.5 150 611944-Ch26.F.indd 150 4/20/10 1:48 PM Chapter 27 Create your own objects with JavaScript In This Chapter ❑ JavaScript Objects ❑ Creating Your Own Objects Objects are useful to organize information. JavaScript Objects Earlier in this book, you learned that JavaScript has several built-in objects, like String, Date, Array, and more. In addition to these built-in objects, you also can create your own. An object is just a special kind of data, a collection of properties and methods. Let’s illustrate with an example and create an object that models a person. Properties are the values associated with the object. The person’s properties include name, height, weight, age, skin tone, eye color, and so on. All persons have these properties, but the values of those properties differ from person to person. Objects also have methods. Methods are the actions that can be performed on objects. The person’s methods could be eat(), sleep(), work(), play(), and so on. Properties The syntax for accessing a property of an object is as follows: objName.propName 151 611944-Ch27.F.indd 151 4/20/10 1:48 PM Learn JavaScript and Ajax with w3schools You can add a property to an object by simply giving it a value. Assume that the personObj already exists; you can give it properties named firstname, lastname, age, and eyecolor as follows: personObj.firstname="John"; personObj.lastname="Doe"; personObj.age=30; personObj.eyecolor="blue"; document.write(personObj.firstname); The preceding code generates the following output: John Methods An object also can contain methods. You can call a method with the following syntax: objName.methodName() NOTE Parameters required for the method can be passed between the parentheses. To call a method called sleep() for the personObj: personObj.sleep(); If the sleep() method accepts a parameter for the number of hours, it could be called like this: personObj.sleep(8) Creating Your Own Objects There are two ways to create a new object: You can create a direct instance of an object, or you can create a template of an object. Create a Direct Instance of an Object The following code creates an instance of an object and adds four properties to it: personObj=new Object(); personObj.firstname="John"; 152 611944-Ch27.F.indd 152 4/20/10 1:48 PM Chapter 27: Create Your Own Objects with JavaScript personObj.lastname="Doe"; personObj.age=50; personObj.eyecolor="blue"; Adding a method to the personObj is also simple. The following code adds a method called eat() to the personObj: personObj.eat=eat; In the following example, you create a direct instance of an object. Your results are shown in Figure 27.1. Try it yourself >> Figure 27.1 153 611944-Ch27.F.indd 153 4/20/10 1:48 PM Learn JavaScript and Ajax with w3schools Create a Template of an Object The template defines the structure of an object so that you can more easily create multiple instances of that object: function person(firstname,lastname,age,eyecolor) { this.firstname=firstname; this.lastname=lastname; this.age=age; this.eyecolor=eyecolor; } Notice that the template is just a function. It is also called a constructor. Inside the constructor, you add the properties and methods that will belong to each subsequent instance of the object. When you use person as a constructor for more than one object, you must include the “this” keyword. JavaScript uses “this” to assign the properties to the specific object created with the “new” keyword. In the following example, you create a template for an object. Your results are shown in Figure 27.2. Try it yourself >> 154 611944-Ch27.F.indd 154 4/20/10 1:48 PM Chapter 27: Create Your Own Objects with JavaScript Figure 27.2 After you have the template, you can create new instances of the object, like this: myFather=new person("John","Doe",50,"blue"); myMother=new person("Sally","Rally",48,"green"); You can also add some methods to the person object. This is also done inside the template: function person(firstname,lastname,age,eyecolor) { this.firstname=firstname; this.lastname=lastname; this.age=age; this.eyecolor=eyecolor; this.newlastname=newlastname; } Note that methods are just functions attached to objects. Then you will have to write the newlastname() function: function newlastname(new_lastname) { this.lastname=new_lastname; } The newlastname() function defines the person’s new last name and assigns that to the person. JavaScript knows which person you’re talking about by using “this.” So, now you can write: myMother.newlastname("Doe"). 155 611944-Ch27.F.indd 155 4/20/10 1:48 PM 611944-Ch27.F.indd 156 4/20/10 1:48 PM Section IV AJAX Basic ❑ Chapter 28: AJAX XMLHttpRequest ❑ Chapter 29: AJAX Browser Support ❑ Chapter 30: AJAX—The XMLHttpRequest Object’s Methods and Properties ❑ Chapter 31: AJAX Server 157 611944-Ch28.F.indd 157 4/20/10 2:04 PM 611944-Ch28.F.indd 158 4/20/10 2:04 PM Chapter 28 AJAX XMLHttpRequest In This Chapter ❑ AJAX Uses the XMLHttpRequest Object ❑ The XMLHttpRequest Object ❑ AJAX Example ❑ Your First AJAX Application AJAX Uses the XMLHttpRequest Object To get or send information from/to a database or a file on the server with traditional JavaScript, you will have to make an HTML form. A user will have to click the Submit button to send/get the information and wait for the server to respond. Then a new page will load with the results. Because the server returns a new page each time the user submits input, traditional Web applications can run slowly and tend to be less user friendly. With AJAX, your JavaScript communicates directly with the server through the JavaScript XMLHttpRequest object. With the XMLHttpRequest object, a Web page can make a request to, and get a response from a Web server—without reloading the page. The user will stay on the same page, and he will not notice that scripts request pages or send data to a server in the background. The XMLHttpRequest Object By using the XMLHttpRequest object, a Web developer can update a page with data from the server after the page has loaded! 159 611944-Ch28.F.indd 159 4/20/10 2:04 PM Learn JavaScript and Ajax with w3schools AJAX was made popular in 2005 by Google (with Google Suggest). Google Suggest is using the XMLHttpRequest object to create a very dynamic Web interface: When you start typing in Google’s search box, a JavaScript sends the letters off to a server, and the server returns a list of suggestions. The XMLHttpRequest object is supported in all major browsers (Internet Explorer, Firefox, Chrome, Opera, and Safari). Your First AJAX Application To understand how AJAX works, we will create a small AJAX application. We will create an AJAX application from scratch. The application will use two click buttons to fetch data from a server and display the information in a Web page without reloading the page itself. First, create a small HTML page with a short