nioffer\'life on web

实体和dom内核

ajax tutorial (Asynchronous javascript and xml)
1. 简要历史
ajax只是以前早已存在的一组工具的名称。
主要部分是XMLHttpRequest,javascript 中一个很有用的类。它应用在internet explorer 4.0 以上版本。
在ajax名称变得普遍使用之前，相同概念的XMLHTTP命名也被使用几次。
google 2005在gmail和googlemaps中使用xmlhttprequest有助于这种这种技术的成功，但是还是ajax本身自己的技术让它自己这么流行。
2. 为什么使用ajax
主要为了建立一个快速，动态的站点，也为了节约资源。
为了改善资源的共享，最好是利用客户机电脑的能力而不是仅仅依靠单独的服务器和网络。ajax 允许客户端使用javascript处理服务器发送过来的数据。从前仅仅是服务端利用web服务或者php scripts处理这种过程，此后通过网络把服务端生成的页面发送到客户机。但是ajax能够有选择性的修改浏览器器中页面的一个部分，更新它而不需要重新装载包含如 图片，菜单等等的整个文档页面。例如：表单的一个项目，用户的选择能够及时的处理并且在同一个页面上无刷新的显示。
3ajax的内涵
ajax是web浏览器支持的一组技术集合，包括以下几个元素“
a：表现层的html和css。
b:客户机使用javascript(ecmascript)处理数据，使用dom对象访问页面的元素或者读取服务器中的xml文件（例如使用getelementbytagname）。
c：使用xmlhttprequest类异步从服务器读取和传递数据。
以下可能被使用
d：domparser类可能被使用。
e：php或者其他在服务器端使用的脚本语言、
f：如果返回一个xml表单，需要使用xml和xslt处理数据。
g：soap可能被用来与服务器会话。
注：异步的含义是在服务器响应的过程中，不需要等待页面或者暂停页面的显示。
3 ajax 的工作机能
ajax使用一种基于显示和事件编程模型，这些事件就是用户的行为动作，它们引发和这些与web页面元素相关联的函数。表单和button按钮帮助实现交互性，dom允许这些动作与页面元素链接起来，当让也能够从服务器提供的xml文件中获取数据。
为了从服务器获取数据，、Xmlhttprequest 对象提供两个方法：
--open：创建与服务器的链接
--send：向服务器发送请求
服务器发回的请求会保存在xmlhttprequest对象的两个属性里
--responseXml 对应于xml格式文档
--responseText 对应于无格式的text文本
。。。在这里注意每处理一个文档要创建一个新的XMLHttpRequest对象。。。
接下来我们必须等待在数据可以使用的时候访问处理它，由此xmlhttprequest对象给出了它的readyState属性来标志数据的状态。readState有5个值
0：还没有初始化。
1：建立链接中
2：请求接收到
3: 结果处理中
4：请求完成
3. ajax与dhtml

Dhtml（动态html） 和 ajax有相似的意图，也是一组关于如下的标准：
--html
--css
--javascript
dhtml允许用户使用输入文本命令改变web页面的显示方式。ajax也允许异步向服务器发送请求和装载数据。
XMLHttpRequest类
属性
readState 0-4
status 200 代表ok 404说明没有找到请求页面。
responseText 返回文本数据
responseXml 返回xml数据类型，可以使用dom方法对它进行解析。
onreadstatechange 接收一个方法作为参数，当readstatechange 改变是自动调用。
方法
open（mode，url，boolean） mode 请求类型，GET或者POST 必须大写。url 请求的页面地址。boolean：true代表异步，false代表同步。后面也可以接收用户名密码参数做为可选择项目。
send（“string”） 如过是GET模式的话 send（null），否则是要向服务器传送的字符串。
一步一步建立一个请求
1.建立实例
if (window.XMLHttpRequest) // window-当前窗口对象
{
xhr = new XMLHttpRequest(); // Firefox, Safari, ...
}
else
if (window.ActiveXObject) // ActiveX 版本
{
xhr = new ActiveXObject("Microsoft.XMLHTTP"); // Internet Explorer
}
当然可能出现异常，修改获得异常信息
try {
xhr = new ActiveXObject("Microsoft.XMLHTTP"); // Trying Internet Explorer
}
catch(e) // Failed
{
xhr = new XMLHttpRequest()
}
第二 等待响应
响应和进一步的处理被包含在与onreadystatechange属性相关联的方法上。如下
xhr.onreadystatechange = function() { // instructions to process the response };

if (xhr.readyState == 4)
{
// Received, OK
} else
{
// Wait...
}
第三步 发送请求 如下
xhr.open('GET', 'http://www.xul.fr/somefile.xml', true);
xhr.send(null）；

实例演示http://www.notebook-batteries.org/demo/ajax-get.html

Acer travlmate 4600 laptop review

The Acer TravelMate 4600 provides more than enough performance, battery life, and features to satisfy home and small-business users interested in simple tasks such as e-mailing, Web surfing, and document creation. We think its $1,149 price tag is pretty good, though you should know that Acer skimps on phone support. If 24/7 help is important to you, look to slightly more expensive laptops, such as the HP Compaq Presario V4000 or the Gateway M460S.

The TravelMate 4600 falls toward the lighter end of the midsize pack. It weighs 6.4 pounds and measures 13.2 inches wide, 11.2 inches deep, and 1.4 inches thick. By comparison, the HP Compaq Presario V4000 weighs 6.5 pounds, while the Gateway M360X comes in at 6.2 pounds. The TravelMate 4600's three-prong, 0.8-pound AC adapter is about the size of a candy bar cell phone.

The laptop features Acer's signature ergonomically curved keyboard, which makes typing more comfortable. The touch pad is wide enough, but the mouse buttons are uncomfortably small; a large scroll button sits between them. Though the system lacks multimedia controls, it has a handy Wi-Fi on/off button and three configurable quick-launch buttons for applications. It operates quietly, except for the occasionally loud DVD burner and a few noisy spins of the internal fan at bootup.

We liked the TravelMate 4600's large, bright, 15-inch display, but we wish it had a higher native resolution than 1,024x768 (XGA). The system's two speakers on the front edge lacked bass and distorted at full volume.

The TravelMate 4600 includes one of the most complete collections of ports, jacks, and slots that we've seen in a $1,149 laptop. The right edge accommodates an infrared port, one Type II PC Card slot, and a 6-in-1 card reader that supports all of the major flash memory cards. The back edge features a Gigabit Ethernet jack plus ports for four-pin FireWire, S-Video out, docking, VGA, DVI, and USB 2.0. The left edge has headphone, microphone, and 56Kbps modem jacks, three more USB 2.0 ports, and the integrated single-layer DVD burner. This feature selection is slightly better than that of the HP Compaq Presario V4000, which costs $400 more than the TravelMate 4600.

Beyond the Windows XP Professional operating system, you don't get much software with the TravelMate 4600. Acer bundles CyberLink PowerDVD and NTI CD & DVD Maker for disc playback and burning, respectively. The only other application is an Acer utility for managing passwords, power management, and other basic settings. This package is typical for a low-cost laptop.

We tested the TravelMate 4600, one of two preconfigured systems in the TravelMate 4600 series. The TravelMate 4600 has a suggested retail price of $1,149, though we found that most online resellers have priced it at more than $1,200. Still, that's a pretty good deal, considering the system's respectable mix of components, including a fast 2GHz Pentium M 760 processor, 1GB of speedy 533MHz RAM, a huge 100GB hard drive rotating at a decent 5,400rpm, and an Intel 915GM chipset that borrows a maximum 128MB of main memory to use as VRAM.

In Labs' benchmark tests, the TravelMate 4600 took full advantage of its components. It ran 25 percent faster than the $1,579 HP Compaq Presario V4000, which has a slower 4,200rpm hard drive, and 26 percent faster than the $1,370 Gateway M360X, which has a slower 1.7GHz Pentium M 735 processor, just 512MB RAM, and a 4,200rpm hard drive. Though the speed difference might not be obvious when conducting such basic tasks as e-mail and word processing, multitaskers and people who like working with lots of windows open will probably benefit from the TravelMate's additional performance.

The TravelMate 4600 also proved a winner in our Labs' battery-drain tests: its battery lasted for a long 4 hours, 1 minute. Both the Presario V4000 and the M360X held out for about three hours.

We can live with the TravelMate 4600's average one-year warranty, which includes mail-in or carry-in service. But we're disappointed with the company's failure to fulfill its 24/7 phone-support claim. Acer claims that tech-support calls placed outside of "live" hours (Monday through Friday from 7 a.m. to 9 p.m. and weekends from 8 a.m. to 5 p.m. CT) will be returned within the hour. But we called and left a message at 3 p.m. PT on a Sunday, and a tech rep never returned our call. Worse, you can't turn to convenient electronic support features, such as real-time tech-support chats, since Acer doesn't offer them.

Power of Acer travelmate 4600

(Longer bars indicate better performance)

Battery part#Acer LCBTP03003,BT.T5003.001

The Acer LCBTP03003 Battery Type is Li-ion.It can supply more power time than avg battery.It have a capability of 4400Mah and output 14.80 volts.

System configurations:

Acer TravelMate 4600

Windows XP

Pro; 2GHz Intel Pentium M 760;

1GB DDR2 PC4300 SDRAM 533MHz;

Intel 915GM/GMS 910GML

Express 128MB;

Power supplied by Acer lcbtp03003 battery

Seagate ST9100822A 100GB 5,400rpm