1. Chapter 1 The Importance of Frontend Performance

   1. Tracking Web Page Performance

   2. Where Does the Time Go?

   3. The Performance Golden Rule

2. Chapter 2 HTTP Overview

   1. Compression

   2. Conditional GET Requests

   3. Expires

   4. Keep-Alive

   5. There's More

3. Chapter 3 Rule 1: Make Fewer HTTP Requests

   1. Image Maps

   2. CSS Sprites

   3. Inline Images

   4. Combined Scripts and Stylesheets

   5. Conclusion

4. Chapter 4 Rule 2: Use a Content Delivery Network

   1. Content Delivery Networks

   2. The Savings

5. Chapter 5 Rule 3: Add an Expires Header

   1. Expires Header

   2. Max-Age and mod_expires

   3. Empty Cache vs. Primed Cache

   4. More Than Just Images

   5. Revving Filenames

   6. Examples

6. Chapter 6 Rule 4: Gzip Components

   1. How Compression Works

   2. What to Compress

   3. The Savings

   4. Configuration

   5. Proxy Caching

   6. Edge Cases

   7. Gzip in Action

7. Chapter 7 Rule 5: Put Stylesheets at the Top

   1. Progressive Rendering

   2. sleep.cgi

   3. Blank White Screen

   4. Flash of Unstyled Content

   5. What's a Frontend Engineer to Do?

8. Chapter 8 Rule 6: Put Scripts at the Bottom

   1. Problems with Scripts

   2. Parallel Downloads

   3. Scripts Block Downloads

   4. Worst Case: Scripts at the Top

   5. Best Case: Scripts at the Bottom

   6. Putting It in Perspective

9. Chapter 9 Rule 7: Avoid CSS Expressions

   1. Updating Expressions

   2. Working Around the Problem

   3. Conclusion

10. Chapter 10 Rule 8: Make JavaScript and CSS External

    1. Inline vs. External

    2. Typical Results in the Field

    3. Home Pages

    4. The Best of Both Worlds

11. Chapter 11 Rule 9: Reduce DNS Lookups

    1. DNS Caching and TTLs

    2. The Browser's Perspective

    3. Reducing DNS Lookups

12. Chapter 12 Rule 10: Minify JavaScript

    1. Minification

    2. Obfuscation

    3. The Savings

    4. Examples

    5. Icing on the Cake

13. Chapter 13 Rule 11: Avoid Redirects

    1. Types of Redirects

    2. How Redirects Hurt Performance

    3. Alternatives to Redirects

14. Chapter 14 Rule 12: Remove Duplicate Scripts

    1. Duplicate Scripts—They Happen

    2. Duplicate Scripts Hurt Performance

    3. Avoiding Duplicate Scripts

15. Chapter 15 Rule 13: Configure ETags

    1. What's an ETag?

    2. The Problem with ETags

    3. ETags: Use 'Em or Lose 'Em

    4. ETags in the Real World

16. Chapter 16 Rule 14: Make Ajax Cacheable

    1. Web 2.0, DHTML, and Ajax

    2. Asynchronous = Instantaneous?

    3. Optimizing Ajax Requests

    4. Caching Ajax in the Real World

17. Chapter 17 Deconstructing 10 Top Sites

    1. Page Weight, Response Time, YSlow Grade

    2. How the Tests Were Done

    3. Amazon

    4. AOL

    5. CNN

    6. eBay

    7. Google

    8. MSN

    9. MySpace

    10. Wikipedia

    11. Yahoo!

    12. YouTube

1. Colophon

The animal on the cover of High Performance Web Sites is a greyhound.

The fastest dog in the world, a greyhound can reach speeds of up to 45 miles per hour, enabled by its streamlined, narrow body; large lungs, heart, and muscles; double suspension gallop (two periods of a gait when all four feet are off the ground); and the flexibility of its spine. Although greyhounds are incredibly fast, they are actually low-energy dogs and lack endurance, requiring less exercise time than most dogs. For this reason, they're often referred to as "45-mile-per-hour couch potatoes" because when not chasing smaller prey (such as rabbits and cats), they are content to spend their days sleeping.

Greyhounds are one of the oldest breeds of dogs, appearing in art and literature throughout history. In ancient Egypt, greyhounds were often mummified and buried with their owners, and hieroglyphics from 4000 B.C.E. show a dog closely resembling the modern greyhound. In Greek and Roman mythology, greyhounds were often depicted with gods and goddesses. Greyhounds appeared in the writings of Homer, Chaucer, Shakespeare, and Cervantes, and they are the only type of dog mentioned in the Bible. They've long been appreciated for their intelligence, graceful form, athleticism, and loyalty.

During the early 1920s, modern greyhound racing was introduced into the United States. Smaller and lighter than show greyhounds, track greyhounds are selectively bred and usually stand between 25- 29 inches tall and weigh 60 70 pounds. These dogs instinctively chase anything that moves quickly (as they are sighthounds, not bloodhounds), hence the lure--the mechanical hare they chase around the track. Greyhound racing is still a very popular spectator sport in the United States and, like horse racing, is enjoyed as a form of parimutuel gambling.

Greyhound racing is very controversial as the dogs experience little human contact and spend most of their non-racing time in crates. Once greyhounds are too old to race (somewhere between three and five years of age), many are euthanized, though there are now many rescue programs that find homes for retired racers. Because greyhounds are naturally docile and even-tempered, most adjust well to adoption and make wonderful pets.

The cover image is from Cassell's Natural History. The cover font is Adobe ITC Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSans Mono Condensed.The production editors for Book Title, eMatter Edition were Ellie Cutler and Jeff Liggett. Linda Walsh was the product manager. Kathleen Wilson provided design support. Lenny Muellner, Mike Sierra, Erik Ray, and Benn Salter provided technical support. This eMatter Edition was produced with FrameMaker 5.5.6.