High Performance JavaScript

Chapter 10. Tools

Matt Sweeney

Having the right software is essential for identifying bottlenecks in both the loading and running of scripts. A number of browser vendors and large-scale websites have shared techniques and tools to help make the Web faster and more efficient. This chapter focuses on some of the free tools available for:

Profiling

Timing various functions and operations during script execution to identify areas for optimization

Network analysis

Examining the loading of images, stylesheets, and scripts and their effect on overall page load and rendering

When a particular script or application is performing less than optimally, a profiler can help prioritize areas for optimization. This can get tricky because of the range of supported browsers, but many vendors now provide a profiler along with their debugging tools. In some cases, performance issues may be specific to a particular browser; other times, the symptoms may occur across multiple browsers. Keep in mind that the optimizations applied to one browser might benefit other browsers, but they might have the opposite effect as well. Rather than assuming which functions or operations are slow, profilers ensure that optimization time is spent on the slowest areas of the system that affect the most browsers.

While the bulk of this chapter focuses on profiling tools, network analyzers can be highly effective in helping to ensure that scripts and pages are loading and running as quickly as possible. Before diving into tweaking ...