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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Regular Expression Optimization

Incautiously crafted regexes can be a major performance bottleneck (the upcoming section, Runaway Backtracking, contains several examples showing how severe this can be), but there is a lot you can do to improve regex efficiency. Just because two regexes match the same text doesn’t mean they do so at the same speed.

Many factors affect a regex’s efficiency. For starters, the text a regex is applied to makes a big difference because regexes spend more time on partial matches than obvious nonmatches. Each browser’s regex engine also has different internal optimizations.[4]

Regex optimization is a fairly broad and nuanced topic. There’s only so much that can be covered in this section, but what’s included should put you well on your way to understanding the kinds of issues that affect regex performance and mastering the art of crafting efficient regexes.

Note that this section assumes you already have some experience with regular expressions and are primarily interested in how to make them faster. If you’re new to regular expressions or need to brush up on the basics, numerous resources are available on the Web and in print. Regular Expressions Cookbook (O’Reilly) by Jan Goyvaerts and Steven Levithan (that’s me!) is written for people who like to learn by doing, and covers JavaScript and several other programming languages equally.

How Regular Expressions Work

In order to use regular expressions efficiently, it’s important to understand how they work their ...

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