book

Professional, JavaScript® for Web Developers, Second Edition

Name: Professional, JavaScript® for Web Developers, Second Edition
Author: Nicholas C. Zakas
ISBN: 9780470227800

by Nicholas C. Zakas

January 2009

Intermediate to advanced

836 pages

21h 30m

English

Wrox

Read now

Unlock full access

Copyright
About the Author
Credits
Acknowledgments
Foreword
Introduction
0.1. What Does This Book Cover?0.2. Who Is This Book For?0.3. What You Need to Use This Book0.4. How This Book Is Structured0.5. Conventions0.6. Source Code0.7. Errata0.8. p2p.wrox.com
1. What Is JavaScript?
1.1. A Short History1.2. JavaScript Implementations1.2.1. ECMAScript1.2.1.1. ECMAScript Editions1.2.1.2. What Does ECMAScript Conformance Mean?1.2.1.3. ECMAScript Support in Web Browsers1.2.2. The Document Object Model (DOM)1.2.2.1. Why the DOM Is Necessary1.2.2.2. DOM Levels1.2.2.3. Other DOMs1.2.2.4. DOM Support in Web Browsers1.2.3. The Browser Object Model (BOM)1.3. JavaScript Versions1.4. Summary
2. JavaScript in HTML
2.1. The <script> Element2.1.1. Tag Placement2.1.2. Deferred Scripts2.1.3. Changes in XHTML2.1.4. Deprecated Syntax2.1.5. Inline Code versus External Files2.2. Document Modes2.3. The <noscript> Element2.4. Summary
3. Language Basics
3.1. Syntax3.1.1. Case-sensitivity3.1.2. Identifiers3.1.3. Comments3.1.4. Statements3.2. Keywords and Reserved Words3.3. Variables3.4. Data Types3.4.1. The typeof Operator3.4.2. The Undefined Type3.4.3. The Null Type3.4.4. The Boolean Type3.4.5. The Number Type3.4.5.1. Floating-Point Values3.4.5.2. Range of Values3.4.5.3. NaN3.4.5.4. Number Conversions3.4.6. The String Type3.4.6.1. Character Literals3.4.6.2. The Nature of Strings3.4.6.3. Converting to a String3.4.7. The Object Type3.5. Operators3.5.1. Unary Operators3.5.1.1. Increment/Decrement3.5.1.2. Unary Plus and Minus3.5.2. Bitwise Operators3.5.2.1. Bitwise NOT3.5.2.2. Bitwise AND3.5.2.3. Bitwise OR3.5.2.4. Bitwise XOR3.5.2.5. Left Shift3.5.2.6. Signed Right Shift3.5.2.7. Unsigned Right Shift3.5.3. Boolean Operators3.5.3.1. Logical NOT3.5.3.2. Logical AND3.5.3.3. Logical OR3.5.4. Multiplicative Operators3.5.4.1. Multiply3.5.4.2. Divide3.5.4.3. Modulus3.5.5. Additive Operators3.5.5.1. Add3.5.5.2. Subtract3.5.6. Relational Operators3.5.7. Equality Operators3.5.7.1. Equal and Not Equal3.5.7.2. Identically Equal and Not Identically Equal3.5.8. Conditional Operator3.5.9. Assignment Operators3.5.10. Comma Operator3.6. Statements3.6.1. The if Statement3.6.2. The do-while Statement3.6.3. The while Statement3.6.4. The for Statement3.6.5. The for-in Statement3.6.6. Labeled Statements3.6.7. The break and continue Statements3.6.8. The with Statement3.6.9. The switch Statement3.7. Functions3.7.1. Understanding Arguments3.7.2. No Overloading3.8. Summary
4. Variables, Scope, and Memory
4.1. Primitive and Reference Values4.1.1. Dynamic Properties4.1.2. Copying Values4.1.3. Argument Passing4.1.4. Determining Type4.2. Execution Context and Scope4.2.1. Scope Chain Augmentation4.2.2. No Block-Level Scopes4.2.2.1. Variable Declaration4.2.2.2. Identifier Lookup4.3. Garbage Collection4.3.1. Mark-and-Sweep4.3.2. Reference Counting4.3.3. Performance4.3.4. Managing Memory4.4. Summary

5. Reference Types
5.1. The Object Type5.2. The Array Type5.2.1. Conversion Methods5.2.2. Stack Methods5.2.3. Queue Methods5.2.4. Reordering Methods5.2.5. Manipulation Methods5.3. The Date Type5.3.1. Inherited Methods5.3.2. Date-Formatting Methods5.3.3. Date/Time Component Methods5.4. The RegExp Type5.4.1. RegExp Instance Properties5.4.2. RegExp Instance Methods5.4.3. RegExp Constructor Properties5.4.4. Pattern Limitations5.5. The Function Type5.5.1. No Overloading (Revisited)5.5.2. Function Declarations vs. Function Expressions5.5.3. Functions as Values5.5.4. Function Internals5.5.5. Function Properties and Methods5.6. Primitive Wrapper Types5.6.1. The Boolean Type5.6.2. The Number Type5.6.3. The String Type5.6.3.1. Character Methods5.6.3.2. String-Manipulation Methods5.6.3.3. String Location Methods5.6.3.4. String Case Methods5.6.3.5. String Pattern-Matching Methods5.6.3.6. The localeCompare() Method5.6.3.7. The fromCharCode() Method5.6.3.8. HTML Methods5.7. Built-in Objects5.7.1. The Global Object5.7.1.1. URI-Encoding Methods5.7.1.2. The eval() Method5.7.1.3. Global Object Properties5.7.1.4. The Window Object5.7.2. The Math Object5.7.2.1. Math Object Properties5.7.2.2. The min() and max() Methods5.7.2.3. Rounding Methods5.7.2.4. The random() Method5.7.2.5. Other Methods5.8. Summary
6. Object-Oriented Programming
6.1. Creating Objects6.1.1. The Factory Pattern6.1.2. The Constructor Pattern6.1.2.1. Constructors as Functions6.1.2.2. Problems with Constructors6.1.3. The Prototype Pattern6.1.3.1. How Prototypes Work6.1.3.2. Prototypes and the in Operator6.1.3.3. Alternate Prototype Syntax6.1.3.4. Dynamic Nature of Prototypes6.1.3.5. Native Object Prototypes6.1.3.6. Problems with Prototypes6.1.4. Combination Constructor/Prototype Pattern6.1.5. Dynamic Prototype Pattern6.1.6. Parasitic Constructor Pattern6.1.7. Durable Constructor Pattern6.2. Inheritance6.2.1. Prototype Chaining6.2.1.1. Default Prototypes6.2.1.2. Prototype and Instance Relationships6.2.1.3. Working with Methods6.2.1.4. Problems with Prototype Chaining6.2.2. Constructor Stealing6.2.2.1. Passing Arguments6.2.2.2. Problems with Constructor Stealing6.2.3. Combination Inheritance6.2.4. Prototypal Inheritance6.2.5. Parasitic Inheritance6.2.6. Parasitic Combination Inheritance6.3. Summary
7. Anonymous Functions
7.1. Recursion7.2. Closures7.2.1. Closures and Variables7.2.2. The this Object7.2.3. Memory Leaks7.3. Mimicking Block Scope7.4. Private Variables7.4.1. Static Private Variables7.4.2. The Module Pattern7.4.3. The Module-Augmentation Pattern7.5. Summary
8. The Browser Object Model
8.1. The window Object8.1.1. The Global Scope8.1.2. Window Relationships and Frames8.1.3. Window Position8.1.4. Window Size8.1.5. Navigating and Opening Windows8.1.5.1. Popping Up Windows8.1.5.2. Security Restrictions8.1.5.3. Pop-up Blockers8.1.6. Intervals and Timeouts8.1.7. System Dialogs8.2. The location Object8.2.1. Query String Arguments8.2.2. Manipulating the Location8.3. The navigator Object8.3.1. Detecting Plug-ins8.3.2. Registering Handlers8.4. The screen Object8.5. The history Object8.6. Summary
9. Client Detection
9.1. Capability Detection9.2. Quirks Detection9.3. User-Agent Detection9.3.1. History9.3.1.1. Early Browsers9.3.1.2. Netscape Navigator 3 and Internet Explorer 39.3.1.3. Netscape Communicator 4 and Internet Explorer 4–89.3.1.4. Gecko9.3.1.5. WebKit9.3.1.6. Konqueror9.3.1.7. Chrome9.3.1.8. Opera9.3.2. Working with User-Agent Detection9.3.2.1. Identifying the Rendering Engine9.3.2.2. Identifying the Browser9.3.2.3. Identifying the Platform9.3.2.4. Identifying Windows Operating Systems9.3.2.5. Identifying Mobile Devices9.3.2.6. Identifying Game Systems9.3.3. The Complete Script9.3.4. Usage9.4. Summary
10. The Document Object Model
10.1. Hierarchy of Nodes10.1.1. The Node Type10.1.1.1. The nodeName and nodeValue Properties10.1.1.2. Node Relationships10.1.1.3. Manipulating Nodes10.1.1.4. Other Methods10.1.2. The Document Type10.1.2.1. Document Children10.1.2.2. Document Information10.1.2.3. Locating Elements10.1.2.4. Special Collections10.1.2.5. DOM Conformance Detection10.1.2.6. Document Writing10.1.3. The Element Type10.1.3.1. HTML Elements10.1.3.2. Getting Attributes10.1.3.3. Setting Attributes10.1.3.4. The attributes Property10.1.3.5. Creating Elements10.1.3.6. Element Children10.1.4. The Text Type10.1.4.1. Creating Text Nodes10.1.4.2. Normalizing Text Nodes10.1.4.3. Splitting Text Nodes10.1.5. The Comment Type10.1.6. The CDATASection Type10.1.7. The DocumentType Type10.1.8. The DocumentFragment Type10.1.9. The Attr Type10.2. DOM Extensions10.2.1. Rendering Modes10.2.2. Scrolling10.2.3. The children Property10.2.4. The contains() Method10.2.5. Content Manipulation10.2.5.1. The innerText Property10.2.5.2. The innerHTML Property10.2.5.3. The outerText Property10.2.5.4. The outerHTML Property10.2.5.5. Memory and Performance Issues10.3. Working with the DOM10.3.1. Dynamic Scripts10.3.2. Dynamic Styles10.3.3. Manipulating Tables10.3.4. Using NodeLists10.4. Summary
11. DOM Levels 2 and 3
11.1. DOM Changes11.1.1. XML Namespaces11.1.1.1. Changes to Node11.1.1.2. Changes to Document11.1.1.3. Changes to Element11.1.1.4. Changes to NamedNodeMap11.1.2. Other Changes11.1.2.1. Changes to DocumentType11.1.2.2. Changes to Document11.1.2.3. Changes to Node11.1.2.4. Changes to Frames11.2. Styles11.2.1. Accessing Element Styles11.2.1.1. DOM Style Properties and Methods11.2.1.2. Computed Styles11.2.2. Working with Style Sheets11.2.2.1. CSS Rules11.2.2.2. Creating Rules11.2.2.3. Deleting Rules11.2.3. Element Dimensions11.2.3.1. Offset Dimensions11.2.3.2. Client Dimensions11.2.3.3. Scroll Dimensions11.2.3.4. Determining Element Dimensions11.3. Traversals11.3.1. NodeIterator11.3.2. TreeWalker11.4. Ranges11.4.1. Ranges in the DOM11.4.1.1. Simple Selection in DOM Ranges11.4.1.2. Complex Selection in DOM Ranges11.4.1.3. Interacting with DOM Range Content11.4.1.4. Inserting DOM Range Content11.4.1.5. Collapsing a DOM Range11.4.1.6. Comparing DOM Ranges11.4.1.7. Cloning DOM Ranges11.4.1.8. Clean Up11.4.2. Ranges in Internet Explorer11.4.2.1. Simple Selection in IE Ranges11.4.2.2. Complex Selection in IE Ranges11.4.2.3. Interacting with IE Range Content11.4.2.4. Collapsing an IE Range11.4.2.5. Comparing IE Ranges11.4.2.6. Cloning an IE Range11.5. Summary
12. Events
12.1. Event Flow12.1.1. Event Bubbling12.1.2. Event Capturing12.1.3. DOM Event Flow12.2. Event Handlers or Listeners12.2.1. HTML Event Handlers12.2.2. DOM Level 0 Event Handlers12.2.3. DOM Level 2 Event Handlers12.2.4. Internet Explorer Event Handlers12.2.5. Cross-Browser Event Handlers12.3. The Event Object12.3.1. The DOM Event Object12.3.2. The Internet Explorer Event Object12.3.3. Cross-Browser Event Object12.4. Event Types12.4.1. UI Events12.4.2. Mouse Events12.4.2.1. Client Coordinates12.4.2.2. Screen Coordinates12.4.2.3. Modifier Keys12.4.2.4. Related Elements12.4.2.5. Buttons12.4.2.6. Additional Event Information12.4.2.7. Mobile Safari Support12.4.2.8. Accessibility Issues12.4.3. Keyboard Events12.4.3.1. Key Codes12.4.3.2. Character Codes12.4.3.3. The textInput Event12.4.3.4. Keyboard Events on Devices12.4.4. HTML Events12.4.4.1. The load Event12.4.4.2. The unload Event12.4.4.3. The resize Event12.4.4.4. The scroll Event12.4.5. Mutation Events12.4.5.1. Node Removal12.4.5.2. Node Insertion12.4.5.3. Attribute Changes12.4.5.4. Text Changes12.4.6. Proprietary Events12.4.6.1. The contextmenu Event12.4.6.2. The beforeunload Event12.4.6.3. The Mousewheel and DOMMouseScroll Events12.4.6.4. The DOMContentLoaded Event12.4.6.5. The readystatechange Event12.4.6.6. The pageshow and pagehide Events12.4.7. Mobile Safari Events12.4.7.1. The orientationchange Event12.4.7.2. Touch Events12.4.7.3. Gesture Events12.5. Memory and Performance12.5.1. Event Delegation12.5.2. Removing Event Handlers12.6. Simulating Events12.6.1. DOM Event Simulation12.6.1.1. Simulating Mouse Events12.6.1.2. Simulating Keyboard Events12.6.1.3. Simulating Other Events12.6.2. Internet Explorer Event Simulation12.7. Summary
13. Scripting Forms
13.1. Form Basics13.1.1. Submitting Forms13.1.2. Resetting Forms13.1.3. Form Fields13.1.3.1. Common Form-Field Properties13.1.3.2. Common Form-Field Methods13.1.3.3. Common Form-Field Events13.2. Scripting Text Boxes13.2.1. Text Selection13.2.1.1. The select Event13.2.1.2. Retrieving Selected Text13.2.1.3. Partial Text Selection13.2.2. Input Filtering13.2.2.1. Blocking Characters13.2.2.2. Dealing with the Clipboard13.2.3. Automatic Tab Forward13.3. Scripting Select Boxes13.3.1. Options Selection13.3.2. Adding Options13.3.3. Removing Options13.3.4. Moving and Reordering Options13.4. Form Serialization13.5. Rich Text Editing13.5.1. Interacting with Rich Text13.5.2. Rich Text Selections13.5.3. Rich Text in Forms13.6. Summary
14. Error Handling and Debugging
14.1. Browser Error Reporting14.1.1. Internet Explorer14.1.2. Firefox14.1.3. Safari14.1.4. Opera14.1.5. Chrome14.2. Error Handling14.2.1. The try-catch Statement14.2.1.1. The finally Clause14.2.1.2. Error Types14.2.1.3. Usage of try-catch14.2.2. Throwing Errors14.2.2.1. When to Throw Errors14.2.2.2. Throwing Errors versus try-catch14.2.3. The error Event14.3. Error-Handling Strategies14.3.1. Identify Where Errors Might Occur14.3.1.1. Type Coercion Errors14.3.1.2. Data Type Errors14.3.1.3. Communication Errors14.3.2. Distinguishing between Fatal and Nonfatal Errors14.3.3. Log Errors to the Server14.4. Debugging Techniques14.4.1. Logging Messages to a Console14.4.2. Logging Messages to the Page14.4.3. Throwing Errors14.5. Common Internet Explorer Errors14.5.1. Operation Aborted14.5.2. Invalid Character14.5.3. Member Not Found14.5.4. Unknown Runtime Error14.5.5. Syntax Error14.5.6. The System Cannot Locate the Resource Specified14.6. Debugging Tools14.6.1. Internet Explorer Debugger14.6.1.1. Breakpoints14.6.1.2. Stepping through Code14.6.1.3. Watches14.6.1.4. The Console14.6.2. Firebug14.6.2.1. Breakpoints14.6.2.2. Stepping through Code14.6.2.3. Watches14.6.2.4. The JavaScript Console14.6.2.5. Logging Function Calls14.6.3. Drosera14.6.3.1. Breakpoints14.6.3.2. Stepping through Code14.6.4. Opera JavaScript Debugger14.6.4.1. Breakpoints14.6.4.2. Stepping through Code14.6.4.3. The Command Line Tab14.6.5. Other Options14.7. Summary
15. XML in JavaScript
15.1. XML DOM Support in Browsers15.1.1. DOM Level 2 Core15.1.2. The DOMParser Type15.1.3. The XMLSerializer Type15.1.4. DOM Level 3 Load and Save15.1.4.1. Parsing XML15.1.4.2. Other Parsing Modes15.1.4.3. Serializing XML15.1.5. XML in Internet Explorer15.1.5.1. Serializing XML15.1.5.2. Loading XML Files15.1.6. Cross-Browser XML Processing15.2. XPath Support in Browsers15.2.1. DOM Level 3 XPath15.2.1.1. Single Node Results15.2.1.2. Simple Type Results15.2.1.3. Default Type Results15.2.1.4. Namespace Support15.2.2. XPath in Internet Explorer15.2.2.1. Namespace Support in Internet Explorer15.2.3. Cross-Browser XPath15.3. XSLT Support in Browsers15.3.1. XSLT in Internet Explorer15.3.1.1. Simple XSLT Transformations15.3.1.2. Complex XSLT Transformations15.3.2. The XSLTProcessor Type15.3.2.1. Using Parameters15.3.2.2. Resetting the Processor15.3.3. Cross-Browser XSLT15.4. Summary
16. ECMAScript for XML
16.1. E4X Types16.1.1. The XML Type16.1.2. The XMLList Type16.1.3. The Namespace Type16.1.4. The QName Type16.2. General Usage16.2.1. Accessing Attributes16.2.2. Other Node Types16.2.3. Querying16.2.4. XML Construction and Manipulation16.2.5. Parsing and Serialization Options16.2.6. Namespaces16.3. Other Changes16.4. Enabling Full E4X16.5. Summary
17. Ajax and JSON
17.1. The XHR Object17.1.1. XHR Usage17.1.2. HTTP Headers17.1.3. GET Requests17.1.4. POST Requests17.1.5. Browser Differences17.1.5.1. Timeouts17.1.5.2. The load Event17.1.5.3. The progress Event17.1.6. Security17.2. Cross-Domain Requests17.2.1. The XDomainRequest Object17.2.2. Cross-Domain XHR17.3. JSON17.3.1. Using JSON with Ajax17.3.2. Security17.4. Summary
18. Advanced Techniques
18.1. Advanced Functions18.1.1. Scope-Safe Constructors18.1.2. Lazy Loading Functions18.1.3. Function Binding18.1.4. Function Currying18.2. Advanced Timers18.2.1. Repeating Timers18.2.2. Yielding Processes18.2.3. Function Throttling18.3. Custom Events18.4. Drag-and-Drop18.4.1. Fixing Drag Functionality18.4.2. Adding Custom Events18.5. Summary
19. Client-Side Storage
19.1. Cookies19.1.1. Restrictions19.1.2. Cookie Parts19.1.3. Cookies in JavaScript19.1.4. Subcookies19.1.5. Cookie Considerations19.2. Internet Explorer User Data19.3. DOM Storage19.3.1. The Storage Type19.3.2. The sessionStorage Object19.3.3. The globalStorage Object19.3.4. The localStorage Object19.3.5. The StorageItem Type19.3.6. The storage Event19.3.7. Limits and Restrictions19.4. Summary
20. Best Practices
20.1. Maintainability20.1.1. What Is Maintainable Code?20.1.2. Code Conventions20.1.2.1. Readability20.1.2.2. Variable and Function Naming20.1.2.3. Variable Type Transparency20.1.3. Loose Coupling20.1.3.1. Decouple HTML/JavaScript20.1.3.2. Decouple CSS/JavaScript20.1.3.3. Decouple Application Logic/Event Handlers20.1.4. Programming Practices20.1.4.1. Respect Object Ownership20.1.4.2. Avoid Globals20.1.4.3. Avoid Null Comparisons20.1.4.4. Use Constants20.2. Performance20.2.1. Be Scope-Aware20.2.1.1. Avoid Global Lookups20.2.1.2. Avoid the with Statement20.2.2. Choose the Right Approach20.2.2.1. Avoid Unnecessary Property Lookup20.2.2.2. Optimize Loops20.2.2.3. Unrolling Loops20.2.2.4. Avoid Double Interpretation20.2.2.5. Other Performance Considerations20.2.3. Minimize Statement Count20.2.3.1. Multiple Variable Declarations20.2.3.2. Insert Iterative Values20.2.3.3. Use Array and Object Literals20.2.4. Optimize DOM Interactions20.2.4.1. Minimize Live Updates20.2.4.2. Use innerHTML20.2.4.3. Use Event Delegation20.2.4.4. Beware of NodeLists20.3. Deployment20.3.1. Build Process20.3.2. Validation20.3.3. Compression20.3.3.1. File Compression20.3.3.2. HTTP Compression20.4. Summary
21. Upcoming APIs
21.1. The Selectors API21.1.1. The querySelector() Method21.1.2. The querySelectorAll() Method21.1.3. Support and the Future21.2. HTML 521.2.1. Character Set Properties21.2.2. Class-Related Additions21.2.2.1. The getElementsByClassName() method21.2.2.2. The classList Property21.2.3. Custom Data Attributes21.2.4. Cross-Document Messaging21.2.5. Media Elements21.2.6. The <canvas> Element21.2.6.1. Drawing Rectangles21.2.6.2. Drawing Paths21.2.6.3. Drawing Text21.2.6.4. Transformations21.2.6.5. Working with Images21.2.7. Offline Support21.2.8. Changes to History21.2.9. Database Storage21.2.10. Drag-and-Drop21.2.10.1. Drag-and-Drop Events21.2.10.2. Custom Drop Targets21.2.10.3. The dataTransfer Object21.2.10.4. dropEffect and effectAllowed21.2.10.5. Additional Members21.2.11. The WebSocket Type21.2.12. The Future of HTML 521.3. Summary
22. The Evolution of JavaScript
22.1. ECMAScript 4/JavaScript 222.1.1. JavaScript 1.522.1.1.1. Constants22.1.1.2. Getters and Setters22.1.2. JavaScript 1.622.1.2.1. Array Extras22.1.2.2. Array and String Generics22.1.3. JavaScript 1.722.1.3.1. Block-Level and Other Scopes22.1.3.2. Generators22.1.3.3. Iterators22.1.3.4. Array Comprehensions22.1.3.5. Destructuring Assignments22.1.4. JavaScript 1.822.1.4.1. Expression Closures22.1.4.2. Generator Expressions22.1.4.3. Array Reductions22.1.5. JavaScript 1.922.1.6. ECMAScript 4 Proposals22.1.7. Variable Typing22.1.7.1. Strings, Numbers, and Booleans22.1.7.2. Nullability22.1.7.3. Detecting Types22.1.8. Functions22.1.8.1. Rest Arguments22.1.8.2. Optional Arguments22.1.8.3. Generic Functions22.1.9. Defining Types22.1.9.1. Union Types22.1.9.2. Deep Types22.1.9.3. Function Types22.1.9.4. Parameterized Types22.1.9.5. Assigning and Converting Types22.1.10. Classes and Interfaces22.1.10.1. Class Prototypes22.1.10.2. Virtual Properties22.1.10.3. Dynamic Classes22.1.10.4. Static Members22.1.11. Interfaces22.1.12. Inheritance22.1.12.1. Overriding superclass Methods22.1.12.2. Final Classes and Methods22.1.13. Namespaces22.1.14. Packages22.1.15. Other Language Changes22.1.15.1. for-each-in22.1.15.2. Operator Overloading22.1.15.3. Changes to with22.1.15.4. Scoping this22.1.15.5. Strict Mode22.1.15.6. Error Type Detection22.1.15.7. Multiline Strings22.1.15.8. String Indexing and Array Slicing22.1.15.9. Regular Expression Changes22.1.15.10. Property Enumeration Setting22.1.15.11. Keyword Usage22.1.15.12. Date Object Changes22.1.15.13. The Vector Class22.1.15.14. The Map Class22.1.16. The Future of ECMAScript 422.2. ECMAScript 3.122.2.1. Changes to Object Internals22.2.2. Static Object Methods22.2.2.1. Accessing Prototype Information22.2.2.2. Working with Object Properties22.2.3. Object Creation22.2.3.1. Retrieving Property Names22.2.3.2. Object Lock-Down Methods22.2.4. Changes to Functions22.2.4.1. Changes to Other Types22.2.5. Native JSON Support22.2.6. Decimals22.2.6.1. Decimal Operations22.2.6.2. Decimal Comparisons22.2.6.3. Decimal Conversions22.2.6.4. Decimal Math22.2.6.5. Other Decimal Methods22.2.7. Usage Subsets22.2.8. The Future of ECMAScript 3.122.3. Summary
A. JavaScript Libraries
A.1. General LibrariesA.1.1. Yahoo! User Interface Library (YUI)A.1.2. PrototypeA.1.3. The Dojo ToolkitA.1.4. MooToolsA.1.5. jQueryA.1.6. MochiKitA.1.7. Ext JSA.2. Internet ApplicationsA.2.1. RicoA.2.2. qooxdooA.3. Animation and EffectsA.3.1. script.aculo.usA.3.2. moo.fxA.3.3. LightboxA.4. CryptographyA.4.1. JavaScript MD5A.4.2. JavaScrypt
B. JavaScript Tools
B.1. DebuggersB.1.1. Microsoft Script DebuggerB.1.2. Microsoft Script EditorB.1.3. Visual Studio .NETB.1.4. Visual Web Developer ExpressB.1.5. FirebugB.1.6. VenkmanB.1.7. DroseraB.1.8. Web InspectorB.1.9. Aptana DebuggerB.2. ValidatorsB.2.1. JSLintB.2.2. JavaScript Lint prototype chainingB.3. CrunchersB.3.1. JSMinB.3.2. Dojo ShrinkSafeB.3.3. YUI CompressorB.4. Unit TestingB.4.1. JsUnitB.4.2. YUI TestB.4.3. Dojo Object Harness (DOH)B.5. Documentation GeneratorsB.5.1. JsDoc ToolkitB.5.2. YUI DocB.5.3. AjaxDocB.6. Secure Execution EnvironmentsB.6.1. AD safeB.6.2. Caja

Content preview from Professional, JavaScript® for Web Developers, Second Edition

Chapter 4. Variables, Scope, and Memory

The nature of variables in JavaScript, as defined in ECMA-262 Third Edition, is quite unique compared to other languages. Being loosely typed, a variable is literally just a name for a particular value at a particular time. Because there are no rules defining the type of data that a variable must hold, a variable's value and data type can change during the lifetime of a script. Though this is an interesting, powerful, and problematic feature, there are many more complexities related to variables.

Primitive and Reference Values

ECMAScript variables may contain two different types of data: primitive values and reference values. Primitive values are simple pieces of data that are stored in memory on the stack, which is to say that the value is completely stored in one memory location. Reference values, on the other hand, are objects that are stored on the heap, meaning that the value stored in the variable is actually just a pointer to another memory location where the object is stored.

When a value is assigned to a variable, the interpreter must determine if it's a primitive or a reference. The five primitive types were discussed in the previous chapter: Undefined, Null, Boolean, Number, and String. Each of these data types takes up a fixed amount of space, so values can easily be stored on the stack. Doing so also allows for fast variable lookup. These variables are said to be accessed by value, because you are manipulating the actual value stored ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.

Read now

Unlock full access

More than 5,000 organizations count on O’Reilly

O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.

Julian F.

Head of Cybersecurity

I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.

Addison B.

Field Engineer

I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.

Amir M.

Data Platform Tech Lead

I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.

Mark W.

Embedded Software Engineer

Professional: JavaScript® for Web Developers, Third Edition

Publisher Resources

ISBN: 9780470227800Purchase book

Cloud Computing

Data Engineering

Data Science

AI & ML

Programming Languages

Software Architecture

IT/Ops

Security

Design

Business

Soft Skills

Professional, JavaScript® for Web Developers, Second Edition

by Nicholas C. Zakas

Chapter 4. Variables, Scope, and Memory

Primitive and Reference Values

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.