[翻译]High Performance JavaScript(022)
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 encoding data.
本章考察从服务器收发数据最快的技术，以及最有效的数据编码格式。
Data Transmission 数据传输
Ajax, at its most basic level, is a way of communicating with a server without unloading the current page; data can be requested from the server or sent to it. There are several different ways of setting up this communication channel, each with its own advantages and restrictions. This section briefly examines the different approaches and discusses the performance implications of each.
Ajax，在它最基本的层面，是一种与服务器通讯而不重载当前页面的方法，数据可从服务器获得或发送给服务器。有多种不同的方法构造这种通讯通道，每种方法都有自己的优势和限制。本节简要地介绍这些不同方法，并讨论各自对性能的影响。
Requesting Data 请求数据
There are five general techniques for requesting data from a server:
有五种常用技术用于向服务器请求数据：
• XMLHttpRequest (XHR)
• Dynamic scrip
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本文主要是出于有朋友使用我原来写的autocomplete的JS控件。当数据量大的时候，会出现效率极其慢的情况，我在这段时间做出的一些测试也及一些经验，与大家分享，如果有错的地方，还请指出。
经过测试，我们会发现如下的情况或者说的结论，如果您的测试结果与我的不符，请说明原因，以便相互学习。
1）当一个较大的HTML字� ......
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 ......
typeof 是JavaScript的运算符
——返回一个用来表示表达式的数据类型的字符串
typeof[(] expression [)] //typeof语法中的圆括号是可选项
typeof 运算符@import url(../html-vss/msdnie4a.css);
typeof
运算符把类型信息当作字符串返回。typeof
返回值有� ......
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 ......
Recursion Patterns 递归模式
When you run into a call stack size limit, your first step should be to identify any instances of recursion in the code. To that end, there are two recursive patterns to be aware of. The first is the straightforward recursive pattern represented ......
