[翻译]High Performance JavaScript(005)
第二章 Data Access 数据访问
One of the classic computer science problems is determining where data should be stored for optimal reading and writing. Where data is stored is related to how quickly it can be retrieved during code execution. This problem in JavaScript is somewhat simplified because of the small number of options for data storage. Similar to other languages, though, where data is stored can greatly affect how quickly it can be accessed later. There are four basic places from which data can be accessed in JavaScript:
经典计算机科学的一个问题是确定数据应当存放在什么地方，以实现最佳的读写效率。数据存储在哪里，关系到代码运行期间数据被检索到的速度。在JavaScript中，此问题相对简单，因为数据存储只有少量方式可供选择。正如其他语言那样，数据存储位置关系到访问速度。在JavaScript中有四种基本的数据访问位置：
Literal values 直接量
Any value that represents just itself and isn't stored in a particular location. JavaScript can represent strings, numbers, Booleans, objects, arrays, functions, regular expressions, and the special values null and undefined as literals.
直接量仅仅代表自己，而不存储于特定位置。 JavaScript的直接量包括：字符串，数字，布尔值，对象，数组，函数，正则表达式，具有特殊意义的空值，以及未定义。
Variables 变量
Any developer-defined location for storing data created by using the var keyword.
开发人员使用var关键字创建用于存储数据值。
Array items 数组项
A numerically indexed location within a JavaScript Array object.
具有数字索引，存储一个JavaScript数组对象。
Object members 对象成员
A string-indexed location within a JavaScript object.
具有字符串索引，存储一个JavaScript对象。
Each of these data storage locations has a particular cost associated with reading and writing operations involving the data. In most cases, the performance difference between accessing information from a literal value versus a local variable is trivial. Accessing info
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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� ......
calcu() ----函数实现两个数相乘
document.write(); ---打印
document.calc.元素名.value; --获得表单的值
document.表单名。表单元素名。value 为表单赋值
定义函数：
function 名字()
{
//javaScript预语句
}
onClick="函数名"; ......
Dynamic Script Elements 动态脚本元素
The Document Object Model (DOM) allows you to dynamically create almost any part of an HTML document using JavaScript. At its root, the <script> element isn't any different than any other element on a page: references can be retrie ......
XMLHttpRequest Script Injection XHR脚本注入
Another approach to nonblocking scripts is to retrieve the JavaScript code using an XMLHttpRequest (XHR) object and then inject the script into the page. This technique involves creating an XHR object, downloading the JavaScript f ......
