五分钟快速入门Ajax：XMLHttpRequest详解
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Ajax 简明手册是一本由 Dave Crane 所编写的实用指南，专为开发者设计，旨在快速理解并掌握Ajax技术的使用。该手册涵盖了Ajax的核心概念、基础语法以及最新工具和技术。主要内容包括：
1. **理解HTTP**：Ajax基于 Hypertext Transfer Protocol (HTTP)，它解释了Ajax如何利用HTTP在后台与服务器进行异步通信，从而实现页面无需刷新就能获取更新数据。
2. **Tips for Using XHR**：这部分提供了关于XMLHttpRequest (XHR)对象的实用技巧，它是Ajax通信的核心。作者指导读者如何直接操作XHR，或者通过像Prototype或jQuery这样的库简化开发过程。
3. **Ajax and Architecture**：讨论了Ajax在Web应用架构中的角色，如单页应用程序(SPA)和模块化开发，帮助开发者理解Ajax如何融入现代Web开发的体系结构中。
4. **Ajax Toolkits**：介绍了流行的Ajax开发工具包，这些工具集成了对XHR的支持，使得开发者能够更方便地构建交互式Web界面。
5. **Ajax User Interfaces**：详细探讨了如何使用Ajax改进用户体验，比如动态加载内容、实时搜索等，提升网站的响应速度和用户体验。
6. **Hot Tips and more**：提供了许多实用的Ajax技巧和示例，帮助开发者解决实际开发中的问题，快速掌握Ajax的最佳实践。
7. **Authoritative content**：保证了内容的专业性和权威性，由顶级专家撰写，确保信息的准确性和深度。
8. **Latest tools & technologies**：随着技术的不断进步，手册紧跟最新趋势，介绍最新的Ajax技术和框架，保持开发者知识的与时俱进。
9. **Bonus content online**：除了纸质版的手册，还提供在线补充资源，包括视频教程、博客文章和社区支持，以扩展学习路径。
10. **Regular Updates**：每1-2周更新一次，确保信息的新鲜度，持续满足开发者对新技术的需求。
订阅该手册，用户将免费获得这一切内容，对于希望深入学习Ajax的开发者来说，这是一份宝贵的参考资料。无论是初级开发者还是经验丰富的工程师，都能从中受益匪浅。
Getting Started with Ajax
By Dave Crane
CONTENTS INCLUDE:
n
Getting to Know HTTP
n
Tips for Using XHR
n
Ajax and Architecture
n
Ajax Toolkits
n
Ajax User Interfaces
n
Hot Tips and more...
n
Authoritative content
n
Designed for developers
n
Written by top experts
n
Latest tools & technologies
n
Hot tips & examples
n
Bonus content online
n
New issue every 1-2 weeks
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GETTING STARTED
The standard way to do Ajax is to use the XMLHttpRequest object,
known as XHR by its friends. Use XHR directly, or via one of the
helpful Ajax libraries such as Prototype or jQuery. How do we use
XHR “by hand”? To start with, we need to get a reference to it:
We can then open a connection to a URL:
Specify a callback function to receive the response:
and then send the request:
The server may be busy, or the network may be slow. We don’t want
to sit around doing nothing until the response arrives, and because
we’ve assigned the callback function, we don’t have to. That’s the
five-minute guide for the impatient. For those who like to know
the details, we’ve listed the fuller details of the XHR object below.
if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
} else if (window.ActiveXObject) {
xhr = new ActiveXObject(“Microsoft.XMLHTTP”);
}
xhr.onreadystatechange = function(){
processReqChange(req);
}
xhr.send(null);
xhr.open(
“GET”,
“my-dynamic-content.jsp?id=”
+encodeURI(myId),
true
);
Method Name Parameters and Descriptions
open(method, url, async) open a connection to a URL
method = HTTP verb (GET, POST, etc.)
url = url to open, may include querystring
async = whether to make asynchronous request
onreadystatechange assign a function object as callback (similar to onclick,
onload, etc. in browser event model)
setRequestHeader
(namevalue)
add a header to the HTTP request
send(body) send the request
body = string to be used as request body
abort() stop the XHR from listening for the response
readyState stage in lifecycle of response (only populated after send()
is called)
httpStatus The HTTP return code (integer, only populated after
response reaches the loaded state)
responseText body of response as a JavaScript string (only set after
response reaches the interactive readyState)
responseXML body of the response as a XML document object (only
set after response reaches the interactive readyState)
getResponseHeader
(name)
read a response header by name
getAllResponseHeaders() Get an array of all response header names
Getting Started with Ajax www.dzone.com Get More Refcardz! visit refcardz.com
To make use of the XHR to its fullest, we recommend you
become familiar with the workings of the HTTP protocol. Using
Ajax, you have much more control over HTTP than with classic
web app development.
HTTP is a stateless request-response protocol.
n
Both request and response contain headers and an optional
body, which is free text.
n
Only a POST request contains a body.
n
A request defines a verb or method.
n
The Mime type of request and response can be set by the
header Content-type
GETTING TO KNOW HTTP
body
request
headers
browser
body
response
headers
server
Hot
Tip
Not all Microsoft browsers rely on ActiveX.
IE7 provides a native JavaScript XHR, so we
check for that first.
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