JavaScript Programming - Introduction to The "Nothing but a Browser" Approach - Higher Education
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Introduction to
JavaScript Programming
The “Nothing but a Browser” Approach
Eric S. Roberts
Stanford University and Reed CollegeSenior Vice President Courseware Portfolio Management: Inventory Manager: Bruce Boundy
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The author and publisher of this book have used their best efforts in preparing this book. These efforts
include the development, research, and testing of the theories and programs to determine their
effectiveness. The author and publisher make no warranty of any kind, expressed or implied, with regard
to these programs or the documentation contained in this book. The author and publisher shall not be liable
in any event for incidental or consequential damages in connection with, or arising out of, the furnishing,
performance, or use of these programs.
Library of Congress Cataloging-in-Publication Data
Names: Roberts, Eric, author.
Title: Introduction to JavaScript Programming / Eric S. Roberts, Stanford University.
Description: First edition. | Pearson Education, Inc., [2020] | Includes index.
Identifiers: LCCN 2018054226 | ISBN 9780135245859 | ISBN 0135245850
Subjects: LCSH: JavaScript (Computer program language)
Classification: LCC QA76.73.J39 R59 2019 | DDC 005.2/762--dc23
LC record available at https://lccn.loc.gov/2018054226
1 19
ISBN 10: 0-13-524585-0
ISBN 13: 978-0-13-524585-9To Lauren, with love
To the Student
Welcome! By picking up this book, you have taken a step into the world of
computer science. Twenty-five centuries ago, the Chinese philosopher Lao-tzu
observed that the longest journey begins with a single step. This book can be your
beginning.
Computing is a profoundly empowering technology. Jobs are plentiful, salaries
are high, and there are far too few people with the necessary skills to fill those jobs.
Computation, moreover, is transforming almost every discipline, not just in science
and engineering but also across the entire university curriculum. No matter what
field of study you choose, understanding how to use computing effectively will be
of enormous value.
To get you started on your journey into the wonders of computer science, this
book teaches you how to write programs in a language called JavaScript, which is a
central technology for web-based applications. The programs you create as you go
through this book will run in any web browser, including the browser on your
phone. More importantly, however, the book will teach you the fundamental
principles of programming. While it uses JavaScript to illustrate these principles,
they will carry over into any other language that you learn.
As with any skill that is worth knowing, programming will not necessarily come
easily. Many students find computers overwhelming and imagine that computer
science is beyond their reach. Learning the basics of programming, however, does
not require advanced mathematics or a detailed understanding of electronics. What
matters is whether you can progress from the statement of a problem to its solution.
To do so, you must be able to think logically and to express your logic in a form
that the computer can understand. Perhaps most importantly, you must be able to
see the task through to its completion without getting discouraged by difficulties
and setbacks. If you stick with the process, you will discover that reaching the
solution is so exhilarating that it more than makes up for any frustrations along the
way.
I wish you an exciting and empowering journey.
Eric Roberts
Stanford University
January 2019
ivTo the Instructor
This book is designed for use in the first programming course in a typical college or
university curriculum. It covers the material in a traditional first course in computer
science, generically referred to as CS1. The book assumes no prior programming
experience and is appropriate both for prospective computer science majors and for
students in other disciplines who are interested in learning the fundamentals of
programming.
The book uses a programming language called JavaScript, which is one of the
most widely used languages in industry and has become the standard language for
writing interactive web applications. Because of its popularity, JavaScript is built
into every major web browser, which means that any device with a browser can run
JavaScript programs without any additional software. The focus of this text,
however, is on the fundamental concepts of programming rather than the language.
It does not cover all of JavaScript and avoids several aspects of the language that
students are likely to misuse. The subset of JavaScript employed in this book
provides students with more than enough power to write exciting programs that run
in any web browser.
The case for using JavaScript in CS1
As a discipline, computing is always changing. These changes can be profoundly
exciting, particularly for students who have grown up in the digital world. For
educators, the breakneck pace of development creates challenges that invariably
extend even into the earliest levels of the curriculum. As languages, tools, and
paradigms shift, teaching strategies must evolve to remain current.
Two decades ago, the Java programming language, with its support for applets,
looked like the wave of the future and seemed likely to become the standard for
web-based programming. That didn’t happen. By the early 2000s, Java applets had
been abandoned in favor of the ubiquitous blend of JavaScript, HTML, and CSS
that serves as the foundation for web applications today.
Once it was clear that JavaScript had triumphed in the race to become the
language of the web, several of my colleagues and I began to think about using it in
Stanford’s introductory programming course. Much of our original motivation for
choosing JavaScript came from our excitement about a “Nothing but a Browser”
model in which students—even those with no access to computers other than a
smart phone—could work entirely in the web environment. When we began
teaching the JavaScript version of our introductory course, we found that the
browser-based model worked exactly as we envisioned. Students no longer have to
install and use a separate development environment. All they need is a web
vbrowser, which every student has. They are also able to add JavaScript content to
their own web pages, which increases the students’ incentive to learn the material
and encourages them to show off their work.
Beyond the advantages of the web-based model, we were delighted to discover
just how well JavaScript works as a teaching language. Students can master the
essentials of JavaScript much more quickly than their predecessors learned Java.
As Douglas Crockford, who developed the widely used JavaScript Object Notation
described in Chapter 9, observes, JavaScript is “a beautiful, elegant, highly
expressive language,” even though it is often used in the context of other web
technologies that share little of that elegance. If you focus on the JavaScript
language itself, its beauty and elegance make teaching JavaScript much simpler than
teaching other languages, with far fewer confusing details to explain.
The relative simplicity of JavaScript is reflected in the length of this textbook,
which is 30 percent shorter than my Java book for the same course. Despite being
shorter, the JavaScript version covers at least 25 percent more material. In part, the
economy of presentation reflects the fact that JavaScript programs are shorter than
the same programs written in Java. Of even greater importance, however, is the fact
that the parts of those programs that disappear in the transition from Java to
JavaScript are precisely the parts that would have required the most explanation.
Pedagogical approach
Introduction to JavaScript Programming relies on three proven strategies to
maximize students’ understanding. First, it introduces the concepts of programming
using a JavaScript version of Rich Pattis’s wonderful Karel the Robot microworld,
which has gently welcomed Stanford students to the world of programming for
almost 40 years. Although it is possible to skip the Karel chapter, we have found
that the increased conceptual understanding students derive from that introduction
more than repays the time. Second, the book adopts the programming guidelines
recommended by Douglas Crockford in JavaScript: The Good Parts, which outlines
how to write elegant, well-structured programs in JavaScript. Third, the book
presents topics in an order that defers the most challenging topics until students
have the necessary background. For example, the detailed discussion of how
JavaScript works together with other web technologies like HTML and CSS appears
in Chapter 12, after students have already completed chapters on data structures and
inheritance.
viPedagogical features
The text uses the following features to enhance student learning:
• Chapter openers. Every chapter begins with a photograph and short biography
of someone who has had a major impact on computing. These biographies, and
the diverse backgrounds of the people included, emphasize the human side of
computing.
• Key terms. Each new term in the text appears in boldface italic and is followed
immediately by a definition.
• Syntax boxes. Each new syntactic form is summarized in a highlighted box that
appears in the margin of that page.
• Syntax coloring. The major program examples appear in numbered figures that
use syntax coloring to ensure that students can easily differentiate comments,
keywords, and string constants from the rest of the code.
• Source code. The source code for all the sample programs is available on the
web site for the book. The programs, moreover, all run in any browser.
• Chapter summary. Each chapter includes an extensive summary that lists the
key ideas introduced in the chapter.
• Review questions. Each chapter summary is followed by review questions that
provide a self-test of student understanding. Answers to the review questions
appear on the web site.
• Programming exercises. Each chapter ends with an extensive set of exercises
that test whether students understand the chapter material while giving them
opportunities to create exciting applications.
Resources for the instructor
The following resources are available to instructors who adopt this textbook on the
Pearson Instructor Resource Center (http://www.pearsonhighered.com/irc):
• Guide to the instructor. Teachers who adopt the text receive an instructor’s
guide that includes additional examples, recommendations for projects and
programming assignments, hints on pedagogical strategy, and suggestions for
possible variations in the order of presentation.
• Lecture slides. The web-based repository for the book includes a set of slides in
Microsoft® PowerPoint for each of the 12 chapters. These slides illustrate the
key points in each chapter and include detailed animations of the program
examples.
• Solutions to the exercises. Adopters have access to a repository containing
solutions to the programming exercises.
viiResources for students
The following resources are available at www.pearsonhighered.com/cs-resources:
• Program sources. The web site includes the source code for all sample
programs presented in the text. The web pages for those programs also allow
students to run the programs directly in the browser.
• Program animations. For several of the most important sample programs, the
web site makes it possible for students to step through the execution of the
program so they can see it in operation.
• Answers to the review questions. The review questions serve as a self-test that
allows students to check their understanding. The answers to these review
questions are available on the web site.
System requirements
The most important advantage of using JavaScript in an introductory course is that
programs run in any browser that implements HTML 5 and ECMA 6—both of
which are supported by all major browsers today. None of the JavaScript programs
require features from more recent versions of JavaScript and in fact use only
ECMA 6 extensions that are typically supported even in older browsers.
Although it is possible to use the interactive applications on the web site to write
simple programs without using any other tools, many students will find it easier to
use a more powerful text editor to write and edit their programs. Many excellent
editors are freely available on the web, and we have found it best to let students
choose an editor that fits their own needs rather than to impose a particular choice.
viiiAcknowledgments
Many people contributed in different ways to the development of this book. I am
especially indebted to Douglas Crockford, whose book JavaScript: The Good Parts
proved that it is possible to write “beautiful, elegant, highly expressive” programs in
JavaScript and showed his readers how to do so.
I also want to thank colleagues at Stanford who have helped make this book
possible. I am profoundly grateful to Jerry Cain, with whom I taught a pilot version
of a JavaScript-based introductory course in the spring of 2016-17. We learned a
great deal from that exercise and have integrated those insights and understandings
into the final version of this book. In addition to being a wonderful co-teacher,
Jerry has been a tireless reader of this text through many drafts. His amazingly
thorough comments have made it much stronger. I owe considerable thanks as well
to my colleagues Chris Piech, Keith Schwarz, and Marty Stepp for their extensive
contributions to the book. And I also need to thank several generations of section
leaders and the students in the pilot versions of the course, all of whom have helped
make it so exciting to teach this material.
I am grateful to Tracy Johnson, Marcia Horton, Erin Ault, Meghan Jacoby, and
the other members of the team at Pearson for their support on this book as well as
its predecessors over the years. In addition, I deeply appreciate the comments from
reviewers Paul Fodor, Ian Utting, Kristine Christensen, and Zerksis Umrigar, who
offered excellent feedback and suggestions.
As always, my greatest thanks are due to my wife Lauren Rusk, who has again
worked her magic as my developmental editor. Lauren’s expertise has added
considerable clarity and polish to the text. Without her, nothing would ever come
out as well as it should.
ixContents
1 A Gentle Introduction 1
1.1 Introducing Karel 2
1.2 Teaching Karel to solve problems 4
1.3 Control statements 10
1.4 Stepwise refinement 17
1.5 Algorithms in Karel’s world 23
Summary 24
Review questions 26
Exercises 26
2 Introducing JavaScript 39
2.1 Data and types 40
2.2 Numeric data 41
2.3 Variables 44
2.4 Functions 49
2.5 String data 53
2.6 Running JavaScript in the browser 56
2.7 Testing and debugging 61
2.8 Software maintenance 69
Summary 71
Review questions 73
Exercises 76
3 Control Statements 79
3.1 Boolean data 80
3.2 The if statement 85
3.3 The switch statement 88
3.4 The while statement 90
3.5 The for statement 94
3.6 Algorithmic programming 100
3.7 Avoiding fuzzy standards of truth 109
Summary 109
Review questions 110
Exercises 112
x4 Simple Graphics 117
4.1 A graphical version of “Hello World” 118
4.2 Classes, objects, and methods 119
4.3 Graphical objects 123
4.4 The graphics window 133
4.5 Creating graphical applications 135
Summary 144
Review questions 146
Exercises 147
5 Functions 155
5.1 A quick review of functions 156
5.2 Libraries 160
5.3 A library to support randomness 163
5.4 The mechanics of function calls 170
5.5 Recursive functions 176
Summary 187
Review questions 188
Exercises 189
6 Writing Interactive Programs 195
6.1 First-class functions 196
6.2 A simple interactive example 199
6.3 Controlling properties of objects 201
6.4 Responding to mouse events 203
6.5 Timer-based animation 208
6.6 Expanding the graphics library 212
Summary 223
Review questions 224
Exercises 225
7 Strings 235
7.1 Binary representation 236
7.2 String operations 243
7.3 Classifying characters 249
7.4 Common string patterns 251
7.5 String applications 253
7.6 Reading from the console 260
Summary 262
Review questions 263
Exercises 265
xi8 Arrays 273
8.1 Introduction to arrays 274
8.2 Array operations 281
8.3 Using arrays for tabulation 288
8.4 Reading text from files 292
8.5 Multidimensional arrays 294
8.6 Image processing 295
Summary 304
Review questions 305
Exercises 306
9 Objects 313
9.1 Objects in JavaScript 314
9.2 Using objects as maps 317
9.3 Representing points 321
9.4 Rational numbers 330
9.5 Linking objects together 338
Summary 342
Review questions 342
Exercises 343
10 Designing Data Structures 349
10.1 Abstract data types 350
10.2 Implementing a token scanner 351
10.3 Efficiency and representation 358
10.4 Representing real-world data 370
Summary 376
Review questions 377
Exercises 378
11 Inheritance 387
11.1 Class hierarchies 388
11.2 Defining an employee hierarchy 391
11.3 Extending graphical classes 395
11.4 Decomposition and inheritance 399
11.5 Alternatives to inheritance 404
Summary 405
Review questions 406
Exercises 407
xii12 JavaScript and the Web 415
12.1 A simple interactive example 416
12.2 An expanded look at HTML 418
12.3 Controlling style using CSS 426
12.4 Connecting JavaScript and HTML 432
12.5 Storing data in the index.html file 443
Summary 449
Review questions 451
Exercises 452
Index 455
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