Foundation of AJAX 阅读笔记（一）

 

   书如其名，介绍AJAX的基础知识，作为程序员入门非常合适。老外写书一向喜欢追根溯源，本书也不例外，第一章就是Web技术的发展简史，从Internet的起源说起，洋洋洒洒。

    Today we have no fewer than four XML derivatives for creating Web applications (and that doesn’t count the W3C’s XHTML): XUL from Mozilla; XAMJ, an open-source alternative that blends Java into the mix; MXML from Macromedia; and XAML from Microsoft.

    第二章介绍了AJAX的核心技术——XMLHttpRequest对象。

标准的对象方法：

Method	Description
abort()	The current request.
getAllResponseHeaders()	Returns all the response headers for the HTTP request as key/value pairs.
getResponseHeader("header")	Returns the string value of the specified header.
open("method", "url")	Sets the stage for a call to the server. The method argument can be either GET, POST, or PUT. The url argument can be relative or absolute. This method includes three optional arguments.
send(content)	Sends the request to the server.
setRequestHeader("header", "value")	Sets the specified header to the supplied value.
open()	must be called before attempting to set any headers.

 

标准的对象属性：

Property	Description
onreadystatechange	The event handler that fires at every state change, typically a call to a JavaScript function.
readyState	The state of the request. The five possible values are 0 = uninitialized,1 = loading, 2 = loaded, 3 = interactive, and 4 = complete.
responseText	The response from the server as a string.
responseXML	The response from the server as XML. This object can be parsed and examined as a DOM object.
status	The HTTP status code from the server (that is, 200 for OK, 404 for Not Found, and so on).
statusText	The text version of the HTTP status code (that is, OK or Not Found, and so on).

使用XMLHttpRequest对象发送请求的基本过程：

1. 获得XMLHttpRequest.的对象实例；

2. 设置对象的onreadystatechange属性所指向的JavaScript方法，以确定对象变化时执行该方法。

3. 赋值请求的属性。对XMLHttpRequest对象的open()方法参数赋值

4.  发送请求到服务器