A Note on Benchmarking  测试基准说明
    Because a regex's performance can be wildly different depending on the text it's applied to, there's no straightforward way to benchmark regexes against each other. For the best result, you need to benchmark your regexes on test strings of varying lengths that match, don't match, and nearly match.
    因为正则表达式性能因应用文本不同而产生很大差异，没有简单明了的方法可以测试正则表达式之间的性能差别。为得到最好的结果，你需要在各种字符串上测试你的正则表达式，包括不同长度，能够匹配的，不能匹配的，和近似匹配的。
    That's one reason for this chapter's lengthy backtracking coverage. Without a firm understanding of backtracking, you won't be able to anticipate and identify backtracking-related problems. To help you catch runaway backtracking early, always test your regexes with long strings that contain partial matches. Think about the kinds of strings that your regexes will nearly but not quite ma ......

String Trimming  字符串修剪
    Removing leading and trailing whitespace from a string is a simple but common task. Although ECMAScript 5 adds a native string trim method (and you should therefore start to see this method in upcoming browsers), JavaScript has not historically included it. For the current browser crop, it's still necessary to implement a trim method yourself or rely on a library that includes it.
    去除字符串首尾的空格是一个简单而常见的任务。虽然ECMAScript 5添加了原生字符串修剪函数（你应该可以在即将出现的浏览器中看到它们），到目前为止JavaScript还没有包含它。对当前的浏览器而言，有必要自己实现一个修剪函数，或者依靠一个包含此功能的库。
    Trimming strings is not a common performance bottleneck, but it serves as a decent case study for regex optimization since there are a variety of ways to implement it.
    修剪字符串不是一个常见的性能瓶颈，但作为学习正则表达式优化的例子有多种实现方法。
Trimming with ......

第六章  Responsive Interfaces  响应接口
    There's nothing more frustrating than clicking something on a web page and having nothing happen. This problem goes back to the origin of transactional web applications and resulted in the now-ubiquitous "please click only once" message that accompanies most form submissions. A user's natural inclination is to repeat any action that doesn't result in an obvious change, and so ensuring responsiveness in web applications is an important performance concern.
    没有什么比点击页面上的东西却什么也没发生更令人感到挫折了。这个问题又回到了原始网页交互程序和现在已无处不在的提交表单时弹出的“请勿重复提交”消息上面。用户自然倾向于重复尝试这些不发生明显变化的动作，所以确保网页应用程序的响应速度也是一个重要的性能关注点。
    Chapter 1 introduced the browser UI thread concept. As a recap, most browsers have a single process that is shared between JavaScript execution and user interface up ......

Yielding with Timers  用定时器让出时间片
    Despite your best efforts, there will be times when a JavaScript task cannot be completed in 100 milliseconds or less because of its complexity. In these cases, it's ideal to yield control of the UI thread so that UI updates may occur. Yielding control means stopping JavaScript execution and giving the UI a chance to update itself before continuing to execute the JavaScript. This is where JavaScript timers come into the picture.
    尽管你尽了最大努力，还是有一些JavaScript任务因为复杂性原因不能在100毫秒或更少时间内完成。这种情况下，理想方法是让出对UI线程的控制，使UI更新可以进行。让出控制意味着停止JavaScript运行，给UI线程机会进行更新，然后再继续运行JavaScript。于是JavaScript定时器进入了我们的视野。
Timer Basics  定时器基础
    Timers are created in JavaScript using either setTimeout() or setInterval(), and both accept the same arguments: a function to execute and the amount of time to ......

Splitting Up Tasks  分解任务
    What we typically think of as one task can often be broken down into a series of subtasks. If a single function is taking too long to execute, check to see whether it can be broken down into a series of smaller functions that complete in smaller amounts of time. This is often as simple as considering a single line of code as an atomic task, even though multiple lines of code typically can be grouped together into a single task. Some functions are already easily broken down based on the other functions they call. For example:
    我们通常将一个任务分解成一系列子任务。如果一个函数运行时间太长，那么查看它是否可以分解成一系列能够短时间完成的较小的函数。可将一行代码简单地看作一个原子任务，多行代码组合在一起构成一个独立任务。某些函数可基于函数调用进行拆分。例如：
function saveDocument(id){
  //save the document
  openDocument(id)
  writeText(id);
  closeDocument(id);
  //update the UI to indi ......

第七章  Ajax  异步JavaScript和XML
    Ajax is a cornerstone of high-performance JavaScript. It can be used to make a page load faster by delaying the download of large resources. It can prevent page loads altogether by allowing for data to be transferred between the client and the server asynchronously. It can even be used to fetch all of a page's resources in one HTTP request. By choosing the correct transmission technique and the most efficient data format, you can significantly improve how your users interact with your site.
    Ajax是高性能JavaScript的基石。它可以通过延迟下载大量资源使页面加载更快。它通过在客户端和服务器之间异步传送数据，避免页面集体加载。它还用于在一次HTTP请求中获取整个页面的资源。通过选择正确的传输技术和最有效的数据格式，你可以显著改善用户与网站之间的互动。
    This chapter examines the fastest techniques for sending data to and receiving it from the server, as well as the most efficient formats for encodi ......