[翻译]High Performance JavaScript(016)
Regular Expression Optimization 正则表达式优化
Incautiously crafted regexes can be a major performance bottleneck (the upcoming section, "Runaway Backtracking" on page 91, contains several examples showing how severe this can be), but there is a lot you can do to improve regex efficiency. Just because two regexes match the same text doesn't mean they do so at the same speed.
粗浅地编写正则表达式是造成性能瓶颈的主要原因（后面“回溯失控”一节有一些例子说明这是多么严重的问题），但还有很多可以改进正则表达式效率的地方。两个正则表达式匹配相同的文本并不意味着他们具有同等的速度。
Many factors affect a regex's efficiency. For starters, the text a regex is applied to makes a big difference because regexes spend more time on partial matches than obvious nonmatches. Each browser's regex engine also has different internal optimizations.
许多因素影响正则表达式的效率。首先，正则表达式适配的文本千差万别，部分匹配时比完全不匹配所用的时间要长。每种浏览器的正则表达式引擎也有不同的内部优化。
Regex optimization is a fairly broad and nuanced topic. There's only so much that can be covered in this section, but what's included should put you well on your way to understanding the kinds of issues that affect regex performance and mastering the art of crafting efficient regexes.
正则表达式的优化是一个相当广泛和细致入微的话题。本节讨论尽其所能，希望这些内容有助于您理解影响正则表达式性能的各种问题和掌握编写高效正则表达式的艺术。
Note that this section assumes you already have some experience with regular expressions and are primarily interested in how to make them faster. If you're new to regular expressions or need to brush up on the basics, numerous resources are available on the Web and in print. Regular Expressions Cookbook (O'Reilly) by Jan Goyvaerts and Steven Levithan (that's me!) is written for people who like to learn by doing, and
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3、组合构造函数/原型方式写类，采用前面种方式继承
这种方式父类，子类的属性都挂在构造函数里，方法都挂在原型上。
/**
* 父类Polygon:多边形
*/
function Polygon(sides) {
this.sides = sides;
}
Polygon.prototype.setSides = function(s) {this.sides=s;}
/**
* Triangle 三角形
* @param {Object} b ......
Repaints and Reflows 重绘和重排版
Once the browser has downloaded all the components of a page—HTML markup, JavaScript, CSS, images—it parses through the files and creates two internal data structures:
当浏览器下载完所有页面HTML标记，JavaScri ......
Conditionals 条件表达式
Similar in nature to loops, conditionals determine how execution flows through JavaScript. The traditional argument of whether to use if-else statements or a switch statement applies to JavaScript just as it does to other languages. Since different b ......
第五章 Strings and Regular Expressions 字符串和正则表达式
Practically all JavaScript programs are intimately tied to strings. For example, many applications use Ajax to fetch strings from a server, convert those strings into more easily usable JavaScript objects, and ......
