Use the Fast Parts 使用速度快的部分
Even though JavaScript is often blamed for being slow, there are parts of the language that are incredibly fast. This should come as no surprise, since JavaScript engines are built in lower-level languages and are therefore compiled. Though it's easy to blame the engine when JavaScript appears slow, the engine is typically the fastest part of the process; it's your code that is actually running slowly. There are parts of the engine that are much faster than others because they allow you to bypass the slow parts.
虽然JavaScript经常被指责缓慢，然而此语言的某些部分具有难以置信的快速。这不足为奇因为JavaScript引擎由低级语言构建。虽然JavaScript速度慢很容易被归咎于引擎，然而引擎通常是处理过程中最快的部分，实际上速度慢的是你的代码。引擎的某些部分比其它部分快很多，因为它们允许你绕过速度慢的部分。
Bitwise Operators 位操作运算符
Bitwise operators are one of the most frequently misunderstoo ......
第九章
Building and Deploying High-Performance JavaScript Applications
创建并部署高性能JavaScript应用程序
According to a 2007 study by Yahoo!'s Exceptional Performance team, 40%–60% of Yahoo!'s users have an empty cache experience, and about 20% of all page views are done with an empty cache (http://yuiblog.com/blog/2007/01/04/performance-research-part-2/). In addition, another more recent study by the Yahoo! Search team, which was independently confirmed by Steve Souders of Google, indicates that roughly 15% of the content delivered by large websites in the United States is served uncompressed.
根据Yahoo!卓越性能团队在2007年进行的研究，40%-60%的Yahoo!用户没有使用缓存的经验，大约20%页面视图不使用缓存（http://yuiblog.com/blog/2007/01/04/performance-research-part-2/）。另外，由Yahoo!研究小组发现，并由Google的Steve Souders所证实的一项最新研究表明，大约15%的美国大型网站所提供的内容没有压缩。
These facts emphasize the need ......
JavaScript Minification JavaScript紧凑
JavaScript minification is the process by which a JavaScript file is stripped of everything that does not contribute to its execution. This includes comments and unnecessary whitespace. The process typically reduces the file size by half, resulting in faster downloads, and encourages programmers to write better, more extensive inline documentation.
JavaScript紧凑指的是剔除一个JavaScript文件中一切运行无关内容的过程。包括注释和不必要的空格。该处理通常可将文件尺寸缩减到一半，其结果是下载速度更快，并鼓励程序员写出更好，更详细的内联文档。
JSMin (http://www.crockford.com/javascript/jsmin.html), developed by Douglas Crockford, remained the standard in JavaScript minification for a long time. However, as web applications kept growing in size and complexity, many felt it was time to push JavaScript minification a step further. This is the main reason behind the development of the YUI Compres ......
Working Around Caching Issues 关于缓存问题
Adequate cache control can really enhance the user experience, but it has a downside: when revving up your application, you want to make sure your users get the latest version of the static content. This is accomplished by renaming static resources whenever they change.
充分利用缓存控制可真正提高用户体验，但它有一个缺点：当应用程序更新之后，你希望确保用户得到静态内容的最新版本。这通过对改动的静态资源进行重命名实现。
Most often, developers add a version or a build number to filenames. Others like to append a checksum. Personally, I like to use a timestamp. This task can be automated using Ant. The following target takes care of renaming JavaScript files by appending a timestamp in the form of yyyyMMddhhmm:
大多情况下，开发者向文件名中添加一个版本号或开发编号。有人喜欢追加一个校验和。个人而言，我更喜欢时间戳。此任务可用Ant自动完成。下面的目标体通过附加一个 ......
第十章 Tools 工具
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:
当确定脚本加载和运行时的瓶颈所在时，合手的工具是必不可少的。许多浏览器厂商和大型网站分享了一些技术和工具，帮助开发者使网页更快，效率更高。本章关注于这些免费工具：
Profiling 性能分析
Timing various functions and operations during script execution to identify areas for optimization
在脚本运行期定时执行不同函数和操作，找出需要优化的部分
Network analysis 网络分析
Examining the loading of images, stylesheets, and scripts and their effect on overall page load and rendering
检查图片，样式表，和脚本的加载过程，汇报它们对整个页 ......
Firebug
Firefox is a popular browser with developers, partially due to the Firebug addon (available at http://www.getfirebug.com/), which was developed initially by Joe Hewitt and is now maintained by the Mozilla Foundation. This tool has increased the productivity of web developers worldwide by providing insights into code that were never before possible.
对开发人员来说，Firefox是一个时髦的浏览器，部分原因是Firebug插件（http://www.getfirebug.com/）由Joe Hewitt首创现在由Mozilla基金会维护。此工具具有前所未有的代码洞察力，提高了全世界网页开发者的生产力。
Firebug provides a console for logging output, a traversable DOM tree of the current page, style information, the ability to introspect DOM and JavaScript objects, and more. It also includes a profiler and network analyzer, which will be the focus of this section. Firebug is also highly extensible, enabling custom panels to be easily added.
Firebug提供了一个� ......
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