tailieunhanh - Developing Large Web Applications- P25

Developing Large Web Applications- P25:This book presents a number of techniques for applying established practices of good software engineering to web development—that is, development primarily using the disparate technologies of HTML, CSS, JavaScript, and server-side scripting languages. Whereas there are many books on how to use languages, how to use libraries, and how to approach software engineering, this is the first book to codify many of the techniques it presents. These techniques will make the components of your own web applications more reusable, maintainable, and reliable | CHAPTER 9 Performance Ultimately none of the techniques presented in this book would be practical if they didn t provide a solid foundation on which to build large web applications that perform quickly and efficiently. This chapter shows how to use the foundation from the previous chapters to monitor and tweak the performance of your application. You may well get a performance boost simply by following the practices already presented in this book. For example the semantically meaningful HTML presented in Chapter 3 can speed up page display for several reasons. Likewise modular techniques for large-scale PHP see Chapter 7 generally create a faster site than jumping in and out of the PHP interpreter multiple times whenever needed. But every professional web developer devotes time to performance as an end in itself so this chapter shows how performance optimization interacts with the techniques in this book. To guide our discussion we ll explore some of the recommendations presented in High Performance Web Sites O Reilly . This book based on research conducted by Steve Souders at Yahoo suggests that for most websites backend performance accounts for only 10 to 20 percent of the overall time required for a page to load the remaining 80 to 90 percent is spent downloading components for the user interface. By following a set of 14 rules many web applications can be made 20 to 25 percent faster. These statistics emphasize the importance of paying close attention to the performance of how your HTML CSS JavaScript and PHP work together. By utilizing a set of techniques for developing large web applications like the ones in this book you can manage performance with relative ease and in a centralized manner. Tenet 9 Large-scale HTML JavaScript CSS and PHP provide a good foundation on which to build large web applications that perform well. They also facilitate a good environment for capturing site metrics and testing. We begin this chapter by looking at how the techniques for