High Performance Web Sites

CNN

Figure 17-8. http://www.cnn.com

CNN (http://www.cnn.com) is the heaviest of the 10 top web sites in both total page weight (502K) and number of HTTP requests (198!). The main reason for this is the use of images to display text. For example, the image http://i.a.cnn.net/cnn/element/img/1.5/main/tabs/topstories.gif is the text "Top Stories," as shown in Figure 17-9.

Figure 17-9. Text rendered in an image

Over 70 images contain only text. Capturing text as an image allows for a customized appearance that may not be possible with text fonts. The tradeoff, as seen in the download statistics, is an increase in page weight and HTTP requests, resulting in a slower user experience. Also, internationalization is more challenging, as each translation requires a new set of images. Rule 1 tells us that reducing the number of components is the most important step to faster performance. Replacing these images with text would yield the biggest performance improvement for this page.

Similarly, there are 16 images used for CSS backgrounds. If these were combined into a few CSS sprites, as described in Chapter 3, 10 or more HTTP requests would be eliminated. Combining the 10 separate JavaScript files together would eliminate another 9 HTTP requests.

Further, more than 140 of the components in the ...