AJAX入门指南：XMLHttpRequest与实践
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"《AJAX入门指南》由Dave Crane撰写，提供了一本全面深入探讨AJAX技术的实用手册。本书旨在帮助开发人员理解和掌握AJAX（Asynchronous JavaScript and XML）的核心原理，特别是XMLHttpRequest对象（XHR）的使用。书中首先介绍了HTTP基础知识，让读者对异步通信有清晰的认识。
章节中，作者给出了使用XHR的技巧，包括如何直接操作这个对象，以及通过像Prototype或jQuery这样的辅助库简化操作。开发者可以学习到如何创建连接、设置回调函数来处理响应，并发送请求。这些操作展示了AJAX的基本工作流程，即使对于初次接触AJAX的开发者来说，也能快速上手。
深入部分，书本详尽阐述了Ajax与架构的关系，探讨了它如何改变Web应用的交互方式，以及如何利用最新工具和技术提升性能。书中还包含了许多实用的热点提示和示例，帮助读者在实践中更好地理解和运用AJAX。
此外，作者强调了权威性和实用性，确保内容来自顶级专家，提供了最新的技术和趋势。不仅如此，书中还有额外的在线资源和定期更新，确保读者能够紧跟行业发展。对于订阅者，他们还能免费获取更多内容，如Refcardz系列，每1-2周更新一次。
《Getting Started with AJAX》是一本既适合新手快速入门，也适合经验丰富的开发者深化理解的宝典，无论是基础操作还是高级应用，都能在其中找到所需的知识和技巧。"
Getting Started with Ajax
By Dave Crane
CONTENTS INCLUDE:
n
Getting to Know HTTP
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Tips for Using XHR
n
Ajax and Architecture
n
Ajax Toolkits
n
Ajax User Interfaces
n
Hot Tips and more...
n
Authoritative content
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Designed for developers
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Written by top experts
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Latest tools & technologies
n
Hot tips & examples
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Bonus content online
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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
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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.
tech facts at your fingertips
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