Learn How to Program Using Any Web Browser

354 Pages·2003·11.78 MB·English

by  Harold Davis

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.
.Learn How to Program Using Any Web Browser
by Harold Davis ISBN:1590591135
Apress © 2004
This text outlines the general principles of good programming practice for complete novices. It
teaches modern computer programming and explains concepts such as object-oriented
programming so that everyone can understand them.
Table of Contents
Learn How to Program Using Any Web Browser
Foreword
Chapter 1 - Getting Started
Chapter 2 - Understanding Types, Variables, and Statements
Chapter 3 - Using Conditional Statements
Chapter 4 - Working with Loops
Chapter 5 - Understanding Functions
Chapter 6 - Programming with Arrays
Chapter 7 - Working with Objects
Chapter 8 - Understanding Events and Event-Driven Programming
Chapter 9 - Manipulating Strings
Chapter 10 - Debugging and Exceptions
Chapter 11 - Programming with JavaScript
Index
List of Figures
List of Tables
List of Examples
List of Sidebars
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Back Cover
For complete novices
No special equipment or software needed beyond a Web browser
Teaches principles of good programming practice
Lots of fun!
Learn How to Program Using Any Web Browser is a book about general principles of good programming practice for
complete novices. If you're a teen or someone who is just starting to get curious about what makes a computer work, or an
office worker who has been using computer applications for years and would like to spend some time looking deeper into
what makes them tick, then this book is for you.
Learn How to Program Using Any Web Browser teaches the basics of programming using JavaScript. JavaScript, a modern
programming language, can be written using any text editor and displayed in almost any web browser, regardless of the
operating system. In the process, author Harold Davis discusses modern computer programming principles and explains
concepts such as object-oriented programming in an easy-to-understand manner.
About the Author
Harold Davis is a technology consultant, hands-on developer, and author of many books. Harold has consulted for Fortune
1000 technology companies, Internet startups, and web infrastructure players. He has been a VP of strategic development at
YellowGiant Corporation, a technical director at Vignette Corporation, and a principal in the e-commerce practice at Informix
Software. He's worked in many languages and environments, and he's been a lead programmer and/or architect in projects
for corporations, including Chase Manhattan Bank, Nike, and Viacom. His books on programming and the web include
Programming C# .NET, Programming Visual Basic .NET, The Wi-Fi Experience: Wireless Networking with 802.11b, Red Hat
Linux 6: Visual QuickPro Guide, Web Developer's Secrets, Delphi Power Toolkit, and more. He has a bachelor's degree in
computer science and mathematics from New York University and a J.D. from Rutgers School of Law.
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Learn How to Program Using Any Web Browser
Harold Davis
Apress
Copyright © 2004 by Harold Davis
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior
written permission of the copyright owner and the publisher.
ISBN (pbk): 1-59059-113-5
Trademarked names may appear in this book. Rather than use a trademark symbol with every occurrence of a
trademarked name, we use the names only in an editorial fashion and to the benefit of the trademark owner, with no
intention of infringement of the trademark.
Technical Reviewer: Beth Christmas
Editorial Board: Dan Appleman, Craig Berry, Gary Cornell, Tony Davis, Steven Rycroft, Julian
Skinner, Martin Streicher, Jim Sumser, Karen Watterson, Gavin Wray, John Zukowski
Assistant Publisher: Grace Wong
Copy Editor: Kim Wimpsett
Production Manager: Kari Brooks
Proofreader: Carol Burbo
Compositor and Artist: Diana Van Winkle, Van Winkle Design
Indexer: Michael Brinkman
Interior and Cover Designer: Kurt Krames
Manufacturing Manager: Tom Debolski
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Germany.
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For information on translations, please contact Apress directly at 2560 Ninth Street, Suite 219, Berkeley, CA 94710.
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The information in this book is distributed on an “as is” basis, without warranty. Although every precaution has been
taken in the preparation of this work, neither the author(s) nor Apress shall have any liability to any person or entity
with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in
this work.
The source code for this book is available to readers at http://www.apress.comin the Downloads section. You will need
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Dedication
For the next generation of potential programmers in my family: Peter, Emma, David, Steven, Julian, and
Nicholas
About the Author
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Harold Davis is a strategic technology consultant, hands-on programmer, and the author of many well-known books.
His books on programming and technology topics include Red Hat Linux 9:Visual QuickPro Guide (Peachpit Press,
2003), Visual Basic .NET for Windows:Visual QuickStart Guide (Peachpit Press, 2003), Visual C# .NET Programming
(Sybex, 2002), Visual Basic .NET Programming (Sybex, 2002), The Wi-Fi Experience: Everyone’s Guide to 802.11b
Wireless Networking (Que, 2001), Visual Basic 6:Visual QuickStart Guide (Peachpit Press, 1999), Red Hat Linux
6:Visual QuickPro Guide (Peachpit Press, 1999), Visual Basic 6 Secrets (IDG Books, 1998), Visual Basic 5 Secrets
(IDG Books, 1997), Visual Basic 4 Secrets (IDG Books, 1996), Web Developer’s Secrets (IDG Books, 1997), and
Delphi Power Toolkit: Cutting-Edge Tools & Techniques for Programmers (Ventana, 1995).
In addition to technical books, Harold has written about a wide range of topics, from art and photography to business
and the stock market. His Publishing Your Art As Cards, Posters & Calendars (Second Edition: Consultant Press,
1996) is the definitive work on the topic and has been in print for more than 20 years.
Harold has served as a technology consultant for many important businesses, including investment funds, technology
companies, and Fortune 500 corporations. In recent years, he was vice president of Strategic Development at
YellowGiant Corporation, chief technology officer at an expert systems company, a technical director at Vignette
Corporation, and a principal in the e-commerce practice at Informix Software.
Harold started programming when he was a child. He has worked in many languages and environments and has been
lead programmer and/or architect in projects for many corporations, including Chase Manhattan Bank, Nike, and
Viacom.
Harold was a professional photographer for 15 years, and he maintained a studio in New York City. His photographs
have been widely exhibited and published. While a professional photographer, he founded Wilderness Studio, a
national distributor of posters and greeting cards.
He has earned a bachelor’s degree in Computer Science and Mathematics from New York University and a doctor’s of
jurisprudence degree from Rutgers Law School, where he was a member of the law review.
Harold lives with his wife, Phyllis Davis, who is also an author, and their two sons, Julian and Nicholas, in the hills of
Berkeley, California. In his spare time he enjoys hiking, gardening, and collecting antique machines including
typewriters and calculation devices.
Acknowledgments
First and foremost, thanks go to my friend Gary Cornell, whose idea this book was. Thanks, Gary, for believing in me!
Second, great thanks go to Grace Wong, without whom this book wouldn’t exist in its current form (dare I say this is
true of most Apress books?).
I also owe a debt of gratitude to Beth Christmas, Martin Davis, and Phyllis Davis, each of whom read this book
carefully in manuscript and made many helpful suggestions.
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Foreword
Programs drive the world. Literally. Heck, there’s more software in the average car than was used to run an airline
when I grew up in the ’60s. But it sure is a different world than when I grew up. And that’s nowhere more so than in the
programming world. When I learned programming in the ’70s, it was all punch cards and big machines—no PCs and
no Internet.
But, too many books that try to teach you programming haven’t gotten the message that it’s a different world: It’s the
world of the Internet! Why, they still use an archaic language called BASIC that’s 40 years old and was designed for
Teletype machines to teach you programming. The book you have in your hand is unusual because it accepts that the
programming world has changed. The browser is all-important: Controlling your browser isn’t only an exciting way to
learn to program, it’s darn useful if you ever want to make your own home page interactive.
But that isn’t the only way this book is different from all the other beginning programming books out there that use
BASIC. Feeding you BASIC as your first programming language is a terrible idea. Why? Because the BASIC
programming language is old and tired and doesn’t use objectoriented programming (OOP) as its fundamental
paradigm. OOP was developed in the ’80s and ’90s, and every programmer must be familiar with it. OOP is how
programmers can hope to piece together the very large programs they need to build in the 21st century.
(If you’re wondering what OOP is, well, you’ll just have to read this book—I won’t try to explain it here because then I’d
have to do a better job than Harold Davis does in this book, and that’s not likely to happen.)
So sit back in front of any computer (heck, even some personal digital assistants) and learn to program by taking full
control of your browser (fun!) and learning OOP (useful!) with one of the best writers I know.
Gary Cornell
Apress, Publisher/Author/Cofounder
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Chapter 1: Getting Started
Overview
If you’ve picked up this book, it’s a pretty good guess that you’d like to learn how to program. Well, you’ve come to the
right place!
This book will teach you the basics of programming. Because this book emphasizes good programming practices, you
won’t learn any bad habits that you might have to “unlearn” later. Programming is—among other things—a craft. Learn
How to Program will teach you the right way to start learning that craft.
You’ll learn how to program with a minimum of fuss and aggravation.
If you have a computer, you won’t have to buy fancy new equipment or software. Best of all, the entire process will be
great fun.
So, what are you waiting for? Let’s get started!
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What Is Programming?
There are many ways to “talk” to a computer. You’re probably already familiar with some of them. For example, most
likely you’ve “surfed” the Web or created a document using Microsoft Word. You may also have used a voicemail
system to leave someone at a big corporation a message or even to check your bank account balance. Indeed, it’s
hard to do anything in the modern world without communicating with computers.
Programming is a particular way of “talking” with a computer that tells the computer to do something. For example,
when you tell your VCR to record a show, you are, of course, programming the VCR.
To take this one step further, each of the examples mentioned earlier— surfing the Web, using a word processor, and
navigating an automated phone system—involve using a program created by someone else. The programmer designs
the program—the Web browser, word processor, or whatever—so that you can achieve results without having to
program anything yourself. The mechanism that you—as opposed to the programmer —use to communicate with the
computer is often called a user interface. Many, if not most, computer programs provide a user interface that allows
users to interact with the computer nonprogrammatically, often using a visual metaphor such as clicking buttons with a
mouse.
This has several interesting implications. First, someone who programs a computer has to think about how a computer
interacts with the instructions that make up a computer program. Second, the programmer has to manage how people
interact with the program.
The point is that programmers interact with computers in a different— some would say deeper and more
significant—way than those who only use programs created by someone else.
To drive this home, think of a game that involves racing cars around a speedway. The programmer has created code
that lets the game interact with a computer on which it’s running. The programmer has to also deliver appropriate
effects when a user chooses a car, steers and accelerates with a game stick or other device, and so on. Figure 1-1
shows this relationship.
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Figure 1-1: A program, such as a racing game, interacts with both a computer and users and makes sure that
the computer takes the steps requested by the users.
Programmers Can Be Users
In some cases, programmers may be the only people interacting with a particular program. But when they do so,
they’re interacting as mere users, not as the programmer who is telling the computer what to do.
Understanding Machine Language, Assembly Language, Operating Systems, and All That
From the viewpoint of this book, you don’t really need to know much about machine language, assembly
language, operating systems, and all that stuff. But, in case you’re curious, machine language is the underlying
two-position native language of computers. You can think of these two positions as a switch with an on and off
(or as a zero and a one). The two positions are also called binary. Machine language manipulates groups of
these switches.
Assembly language, also sometimes called assembler, is a somewhat more human-friendly mechanism that can
directly communicate with the hardware switches that natively “think” in machine language. Assembly language
is specific to a particular processor because its statements correspond to specific machine instructions.
Assembly and machine language are considered low-level languages—they allow direct access to all of the
capabilities of the underlying system, but they’re time consuming and tedious to use. In contrast, the
programming languages described in the next section are considered high level because they hide the actual
low-level details of how something is implemented and combine many low-level commands into single
statements.
Operating systems are computer programs—such as Microsoft Windows or Linux—whose principal purposes
are to launch other programs, give them resources to run, and keep them out of each other’s way. Operating
systems vary greatly in functionality and sophistication. Most also provide a high-level mechanism for
programmers to utilize underlying system capabilities to perform tasks such accessing files on a disk.
Exploring Programming Languages
Programming languages are the way programmers communicate with computers. As you’ll see in this book, in some
sense computers aren’t inherently very bright. The programmer generally supplies the smarts— which can range from
nonexistent to vast.
In the words of Tolstoy, “Happy families are all alike.” Similarly, all modern high-level programming languages are
really pretty much alike.
To say that all programming languages are pretty much alike might evoke gasps of horror from adherents of one
language or another—and, truthfully, it’s an exaggeration because some important differences exist between
languages. However, it’s not a bad generalization.
Like human languages, computer programming languages use specific words, often called keywords, to mean specific
things. Keywords are typically human-language-like so that their meanings can be intuitive. For example, the keyword
if generally tells the computer to do one thing or another thing depending on how a condition is evaluated. This is
comparable to the English sentence “If it’s after 3 P.M., pick up the baby.”
In other words, the If in the sentence tells someone to check the time and, if it meets the condition (it’s after 3 P.M.), to
do something (pick up the baby).
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In human languages, rules of grammar and syntax are used to put words together into phrases and sentences, such
as the example sentence “If it’s after 3 P.M., pick up the baby.” Then sentences are combined to tell a story, give
directions, or provide a million other purposes.
Computer languages work the same way. In other words, you put keywords and other elements together using rules of
syntax to create statements. (You can think of a statement as a sentence in a computer program.)
These statements combine to create computer programs.
The syntax of a programming language is the basic scaffolding you use to create programs and applications with that
language. Understanding the syntax means understanding how a language works—and knowing what the language
can (and can’t) do.
If you learn a foreign language, then you can communicate with natives who speak that language. Similarly, if you
learn the language of computers, you can “speak” with a computer. Just as it helps to learn a foreign language by
thinking the way native speakers do, it helps to learn to think like a computer if you want to learn a computer’s
language. (So, really, this book is about computer psychology.)
However, before a computer can run a computer program that’s written in a human-like language, the program needs
to be translated into code that the machine understands. Programmers accomplish this using special programs called
compilers and interpreters.
Understanding Compilers, Interpreters, and Why Not to Worry
A compiler translates a high-level program into machine code and creates an executable program that can be
processed by the machine. In contrast, an interpreter translates program statements in code that can be
processed by the computer on the fly, a kind of “pay-as-you-go” scenario.
Although professional programmers may have to worry quite a bit about the nature of the compiler or interpreter
they’re working with, often these programs are built into the development environment used to create the
program.
In the case of the programs you’ll write using this book, you don’t have to worry about these things at all
because JavaScript—the language used in this book—has an interpreter built into every modern Web browser.