Credits
Preface
1. Understanding Ajax Performance
Trade-offs
Principles of Optimization
Ajax
Browser
Wow!
JavaScript
Summary

2. Creating Responsive Web Applications
What Is Fast Enough?
Measuring Latency
When Latency Goes Bad
Threading
Ensuring Responsiveness
Web Workers
Gears
Timers
Effects of Memory Use on Response Time
Virtual Memory
Troubleshooting Memory Issues
Summary

3. Splitting the Initial Payload
Kitchen Sink
Savings from Splitting
Finding the Split
Undefined Symbols and Race Conditions
Case Study: Google Calendar

4. Loading Scripts Without Blocking
Scripts Block
Making Scripts Play Nice
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
Browser Busy Indicators
Ensuring (or Avoiding) Ordered Execution
Summarizing the Results
And the Winner Is

5. Coupling Asynchronous Scripts
Code Example: menu.js
Race Conditions
Preserving Order Asynchronously
Technique 1: Hardcoded Callback
Technique 2: Window Onload
Technique 3: Timer
Technique 4: Script Onload
Technique 5: Degrading Script Tags
Multiple External Scripts
Managed XHR
DOM Element and Doc Write
General Solution
Single Script
Multiple Scripts
Asynchronicity in the Real World
Google Analytics and Dojo
YUI Loader Utility

6. Positioning Inline Scripts
Inline Scripts Block
Move Inline Scripts to the Bottom
Initiate Execution Asynchronously
Use Script Defer
Preserving CSS and JavaScript Order
Danger: Stylesheet Followed by Inline Script
Inline Scripts Aren’t Blocked by Most Downloads
Inline Scripts Are Blocked by Stylesheets
This Does Happen

7. Writing Efficient JavaScript
Managing Scope
Use Local Variables
Scope Chain Augmentation
Efficient Data Access
Flow Control
Fast Conditionals
Fast Loops
String Optimization
String Concatenation
Trimming Strings
Avoid Long-Running Scripts
Yielding Using Timers
Timer Patterns for Yielding
Summary

8. Scaling with Comet
How Comet Works
Transport Techniques
Polling
Long Polling
Forever Frame
XHR Streaming
Future Transports
Cross-Domain
Effects of Implementation on Applications
Managing Connections
Measuring Performance
Protocols
Summary

9. Going Beyond Gzipping
Why Does This Matter?
What Causes This?
Quick Review
The Culprit
Examples of Popular Turtle Tappers
How to Help These Users?
Design to Minimize Uncompressed Size
Educate Users
Direct Detection of Gzip Support

10. Optimizing Images
Two Steps to Simplify Image Optimization
Image Formats
Background
Characteristics of the Different Formats
More About PNG
Automated Lossless Image Optimization
Crushing PNGs
Stripping JPEG Metadata
Converting GIF to PNG
Optimizing GIF Animations
Smush.it
Progressive JPEGs for Large Images
Alpha Transparency: Avoid AlphaImageLoader
Effects of Alpha Transparency
AlphaImageLoader
Problems with AlphaImageLoader
Progressively Enhanced PNG8 Alpha Transparency
Optimizing Sprites
?ber-Sprite Versus Modular Sprite
Highly Optimized CSS Sprites
Other Image Optimizations
Avoid Scaling Images
Crush Generated Images
Favicons
Apple Touch Icon
Summary

11. Sharding Dominant Domains
Critical Path
Who’s Sharding?
Downgrading to HTTP/1.0
Rolling Out Sharding
IP Address or Hostname
How Many Domains
How to Split Resources
Newer Browsers

12. Flushing the Document Early
Flush the Head
Output Buffering
Chunked Encoding
Flushing and Gzip
Other Intermediaries
Domain Blocking During Flushing
Browsers: The Last Hurdle
Flushing Beyond PHP
The Flush Checklist

13. Using Iframes Sparingly
The Most Expensive DOM Element
Iframes Block Onload
Parallel Downloads with Iframes
Script Before Iframe
Stylesheet Before Iframe
Stylesheet After Iframe
Connections per Hostname
Connection Sharing in Iframes
Connection Sharing Across Tabs and Windows
Summarizing the Cost of Iframes

14. Simplifying CSS Selectors
Types of Selectors
ID Selectors
Class Selectors
Type Selectors
Adjacent Sibling Selectors
Child Selectors
Descendant Selectors
Universal Selectors
Attribute Selectors
Pseudo-Classes and Pseudo-Elements
The Key to Efficient CSS Selectors
Rightmost First
Writing Efficient CSS Selectors
CSS Selector Performance
Complex Selectors Impact Performance (Sometimes)
CSS Selectors to Avoid
Reflow Time
Measuring CSS Selectors in the Real World
Appendix: Performance Tools
Index