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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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YUI Profiler

The YUI Profiler (http://developer.yahoo.com/yui/profiler/), contributed by Nicholas Zakas, is a JavaScript profiler written in JavaScript. In addition to timer functionality, it provides interfaces for profiling functions, objects, and constructors, as well as detailed reports of the profile data. It enables profiling across various browsers and data exporting for more robust reporting and analysis.

The YUI Profiler provides a generic timer that collects performance data. Profiler provides static methods for starting and stopping named timings and retrieving profile data.

var count = 10000, i, element;
    Y.Profiler.start('createElement');

    for (i = 0; i < count; i++) {
        element = document.createElement('div');
    }

    Y.Profiler.stop('createElement');

    alert('created ' + count + 'in' +
            Y.Profiler.getAverage('createElement') + 'ms');

This clearly improves upon the inline Date and Timer approach and provides additional profile data regarding the number of times called, as well as the average, minimum, and maximum times. This data is collected and can be analyzed alongside other profile results.

Functions can be registered for profiling as well. The registered function is instrumented with code that collects performance data. For example, to profile the global initUI method from Chapter 2, all that is required is the name:

Y.Profiler.registerFunction("initUI");

Many functions are bound to objects in order to prevent pollution of the global namespace. Object methods can be registered ...

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