You are previewing High Performance JavaScript.

High Performance JavaScript

Cover of High Performance JavaScript by Nicholas C. Zakas Published by O'Reilly Media, Inc.
  1. High Performance JavaScript
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. Preface
      1. The Internet Evolves
      2. Why Optimization Is Necessary
      3. Next-Generation JavaScript Engines
      4. Performance Is Still a Concern
      5. How This Book Is Organized
      6. JavaScript Loading
      7. Coding Technique
      8. Deployment
      9. Testing
      10. Who This Book Is For
      11. Conventions Used in This Book
      12. Using Code Examples
      13. Safari® Books Online
      14. How to Contact Us
      15. Acknowledgments
    3. 1. Loading and Execution
      1. Script Positioning
      2. Grouping Scripts
      3. Nonblocking Scripts
      4. Summary
    4. 2. Data Access
      1. Managing Scope
      2. Object Members
      3. Summary
    5. 3. DOM Scripting
      1. DOM in the Browser World
      2. DOM Access and Modification
      3. Repaints and Reflows
      4. Event Delegation
      5. Summary
    6. 4. Algorithms and Flow Control
      1. Loops
      2. Conditionals
      3. Recursion
      4. Summary
    7. 5. Strings and Regular Expressions
      1. String Concatenation
      2. Regular Expression Optimization
      3. String Trimming
      4. Summary
    8. 6. Responsive Interfaces
      1. The Browser UI Thread
      2. Yielding with Timers
      3. Web Workers
      4. Summary
    9. 7. Ajax
      1. Data Transmission
      2. Data Formats
      3. Ajax Performance Guidelines
      4. Summary
    10. 8. Programming Practices
      1. Avoid Double Evaluation
      2. Use Object/Array Literals
      3. Don’t Repeat Work
      4. Use the Fast Parts
      5. Summary
    11. 9. Building and Deploying High-Performance JavaScript Applications
      1. Apache Ant
      2. Combining JavaScript Files
      3. Preprocessing JavaScript Files
      4. JavaScript Minification
      5. Buildtime Versus Runtime Build Processes
      6. JavaScript Compression
      7. Caching JavaScript Files
      8. Working Around Caching Issues
      9. Using a Content Delivery Network
      10. Deploying JavaScript Resources
      11. Agile JavaScript Build Process
      12. Summary
    12. 10. Tools
      1. JavaScript Profiling
      2. YUI Profiler
      3. Anonymous Functions
      4. Firebug
      5. Internet Explorer Developer Tools
      6. Safari Web Inspector
      7. Chrome Developer Tools
      8. Script Blocking
      9. Page Speed
      10. Fiddler
      11. YSlow
      12. dynaTrace Ajax Edition
      13. Summary
    13. Index
    14. About the Author
    15. Colophon
    16. SPECIAL OFFER: Upgrade this ebook with O’Reilly
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Chapter 2. Data Access

One of the classic computer science problems is determining where data should be stored for optimal reading and writing. Where data is stored is related to how quickly it can be retrieved during code execution. This problem in JavaScript is somewhat simplified because of the small number of options for data storage. Similar to other languages, though, where data is stored can greatly affect how quickly it can be accessed later. There are four basic places from which data can be accessed in JavaScript:

Literal values

Any value that represents just itself and isn’t stored in a particular location. JavaScript can represent strings, numbers, Booleans, objects, arrays, functions, regular expressions, and the special values null and undefined as literals.

Variables

Any developer-defined location for storing data created by using the var keyword.

Array items

A numerically indexed location within a JavaScript Array object.

Object members

A string-indexed location within a JavaScript object.

Each of these data storage locations has a particular cost associated with reading and writing operations involving the data. In most cases, the performance difference between accessing information from a literal value versus a local variable is trivial. Accessing information from array items and object members is more expensive, though exactly which is more expensive depends heavily on the browser. Figure 2-1 shows the relative speed of accessing 200,000 values from each of these four ...

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