Table Of ContentJavaScript Enlightenment
Cody Lindley
JavaScript Enlightenment
by Cody Lindley
Copyright © 2013 Cody Lindley. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are
also available for most titles (http://my.safaribooksonline.com). For more information, contact our corporate/
institutional sales department: 800-998-9938 or [email protected].
Editors: Simon St. Laurent and Meghan Blanchette Proofreader: BIM Proofreading Services
Production Editor: Kristen Borg Indexer: Ellen Troutman Zaig
Cover Designer: Randy Comer
Interior Designer: David Futato
January 2013: First Edition
Revision History for the First Edition:
2012-12-18 First release
See http://oreilly.com/catalog/errata.csp?isbn=9781449342883 for release details.
Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of O’Reilly
Media, Inc. JavaScript Enlightenment, the image of a Eurasian eagle owl, and related trade dress are trade‐
marks of O’Reilly Media, Inc.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as
trademarks. Where those designations appear in this book, and O’Reilly Media, Inc., was aware of a trade‐
mark claim, the designations have been printed in caps or initial caps.
While every precaution has been taken in the preparation of this book, the publisher and author assume no
responsibility for errors or omissions, or for damages resulting from the use of the information contained
herein.
ISBN: 978-1-449-34288-3
[LSI]
Table of Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
1. JavaScript Objects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Creating Objects 1
JavaScript Constructors Construct and Return Object Instances 6
The JavaScript Native/Built-In Object Constructors 8
User-Defined/Non-Native Object Constructor Functions 9
Instantiating Constructors Using the new Operator 10
Creating Shorthand/Literal Values from Constructors 12
Primitive (a.k.a. Simple) Values 13
The Primitive Values null, undefined, “string”, 10, true, and false Are Not
Objects 15
How Primitive Values Are Stored/Copied in JavaScript 16
Primitive Values Are Equal by Value 17
The String, Number, and Boolean Primitive Values Act Like Objects When
Used Like Objects 18
Complex (a.k.a. Composite) Values 19
How Complex Values Are Stored/Copied in JavaScript 20
Complex Objects Are Equal by Reference 21
Complex Objects Have Dynamic Properties 22
The typeof Operator Used on Primitive and Complex Values 22
Dynamic Properties Allow for Mutable Objects 23
All Constructor Instances Have Constructor Properties that Point to Their
Constructor Function 24
Verify that an Object Is an Instance of a Particular Constructor Function 26
An Instance Created From a Constructor Can Have Its Own Independent
Properties (Instance Properties) 27
The Semantics of “JavaScript Objects” and “Object() Objects” 29
2. Working with Objects and Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
iii
Complex Objects Can Contain Most of the JavaScript Values as Properties 31
Encapsulating Complex Objects in a Programmatically Beneficial Way 32
Getting/Setting/Updating an Object’s Properties Using Dot Notation or
Bracket Notation 33
Deleting Object Properties 36
How References to Object Properties Are Resolved 36
Using hasOwnProperty, Verify That an Object Property Is Not From the
Prototype Chain 39
Checking If an Object Contains a Given Property Using the in Operator 39
Enumerate (Loop Over) an Object’s Properties using the for in Loop 40
Host Objects versus Native Objects 41
Enhancing and Extending Objects with Underscore.js 43
3. Object(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Conceptual Overview of Using Object() Objects 45
Object() Parameters 46
Object() Properties and Methods 47
Object() Object Instance Properties and Methods 47
Creating Object() Objects Using “Object Literals” 48
All Objects Inherit From Object.prototype 49
4. Function(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Conceptual Overview of Using Function() Objects 51
Function() Parameters 52
Function() Properties and Methods 53
Function Object Instance Properties and Methods 53
Functions Always Return a Value 53
Functions Are First-Class Citizens (Not Just Syntax but Values) 54
Passing Parameters to a Function 55
this and arguments Values Available To All Functions 55
The arguments.callee Property 56
The Function Instance length Property and arguments.length 57
Redefining Function Parameters 58
Return a Function Before It Is Done (Cancel Function Execution) 58
Defining a Function (Statement, Expression, or Constructor) 59
Invoking a Function [Function, Method, Constructor, or call() and apply()] 60
Anonymous Functions 61
Self-Invoking Function Expression 61
Self-Invoking Anonymous Function Statements 62
Functions Can Be Nested 62
Passing Functions to Functions and Returning Functions from Functions 63
Invoking Function Statements Before They Are Defined (Function Hoisting) 64
iv | Table of Contents
A Function Can Call Itself (Recursion) 64
5. The Head/Global Object. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Conceptual Overview of the Head Object 67
Global Functions Contained Within the Head Object 68
The Head Object versus Global Properties and Global Variables 68
Referring to the Head Object 70
The Head Object Is Implied and Typically Not Referenced Explicitly 70
6. The this Keyword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Conceptual Overview of this and How It Refers to Objects 73
How Is the Value of this Determined? 74
The this Keyword Refers to the Head Object in Nested Functions 76
Working Around the Nested Function Issue by Leveraging the Scope Chain 77
Controlling the Value of this Using call() or apply() 77
Using the this Keyword Inside a User-Defined Constructor Function 79
The this Keyword Inside a Prototype Method Refers to a Constructor Instance 80
7. Scope and Closures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Conceptual Overview of JavaScript Scope 83
JavaScript Does Not Have Block Scope 84
Use var Inside Functions to Declare Variables and Avoid Scope Gotchas 85
The Scope Chain (Lexical Scoping) 85
The Scope Chain Lookup Returns the First Found Value 87
Scope Is Determined During Function Definition, not Invocation 87
Closures Are Caused by the Scope Chain 88
8. Function Prototype Property. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Conceptual Overview of the Prototype Chain 91
Why Care About the prototype Property? 92
Prototype Is Standard on All function() Instances 93
The Default prototype Property Is an Object() Object 93
Instances Created From a Constructor Function are Linked to the
Constructor’s prototype Property 94
Last Stop in the prototype Chain is Object.prototype 95
The prototype Chain Returns the First Property Match It Finds in the Chain 96
Replacing the prototype Property with a New Object Removes the Default
Constructor Property 96
Instances That Inherit Properties from the Prototype Will Always Get the
Latest Values 97
Replacing the prototype Property with a New Object Does Not Update
Former Instances 98
Table of Contents | v
User-Defined Constructors Can Leverage the Same Prototype Inheritance as
Native Constructors 99
Creating Inheritance Chains (the Original Intention) 100
9. Array(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Conceptual Overview of Using Array() Objects 103
Array() Parameters 104
Array() Properties and Methods 104
Array Object Instance Properties and Methods 105
Creating Arrays 105
Adding and Updating Values in Arrays 106
Length versus Index 107
Defining Arrays with a Predefined Length 107
Setting Array Length can Add or Remove Values 108
Arrays Containing Other Arrays (Multidimensional Arrays) 108
Looping Over an Array, Backwards and Forwards 109
10. String(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Conceptual Overview of Using the String() Object 111
String() Parameters 111
String() Properties and Methods 112
String Object Instance Properties and Methods 112
11. Number(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Conceptual Overview of Using the Number() Object 115
Integers and Floating-Point Numbers 116
Number() Parameters 116
Number() Properties 117
Number Object Instance Properties and Methods 117
12. Boolean(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Conceptual Overview of Using the Boolean() Object 119
Boolean() Parameters 120
Boolean() Properties and Methods 120
Boolean Object Instance Properties and Methods 121
Non-Primitive False Boolean Objects Convert to true 121
Certain Things Are false, Everything Else Is true 122
13. Working with Primitive String, Number, and Boolean Values. . . . . . . . . . . . . . . . . . . . . 123
Primitive/Literal Values Are Converted to Objects When Properties Are
Accessed 123
vi | Table of Contents
You Should Typically Use Primitive String, Number, and Boolean Values 125
14. Null. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Conceptual Overview of Using the null Value 127
typeof Returns null Values as “object” 127
15. Undefined. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Conceptual Overview of the undefined Value 129
JavaScript ECMAScript 3 Edition (and Later) Declares the undefined Variable
in the Global Scope 130
16. Math Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Conceptual Overview of the Built-In Math Object 131
Math Properties and Methods 131
Math Is Not a Constructor Function 132
Math Has Constants You Cannot Augment/Mutate 133
A. Review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
B. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Table of Contents | vii
