完全了解AJAX(一)

作者:zym007 日期:2006-12-23 16:52:30

字体大小: 小中大

尽管AJAX是个相对新生的术语，但其背后的技术却并不新颖。随着XMLHttpRequest对象在大多数浏览器中的实现，以及GMail和Google Maps的出现激发了软件开发者重新考虑如何构建网页的灵感。我们从基础开始认识AJAX，一种颠覆性的技术，其改变了Web应用程序的开发和应用方式，使得交互性页面和网站处于目前网络潮流的最前沿。

当请求被发送到浏览器后，其所具有的改变网页内容的功能已经存在许多年了-使用javascript脚本改变iframe's src属性是技术之一。

XMLHttpRequest对象

XMLHttpRequest对象使AJAX的出现成为可能，它产生异步请求，并决定如何处理结果。在大多数浏览器中，我们使用如下代码来创建对象：

var xmlhttp = false;

try {

xmlhttp = new XMLHttpRequest();

} catch (e) {

alert("cannot create object");

}

不幸的是，上文中所提到的“大多数浏览器”并不包括IE,因此对于微软的浏览器，我们需要采用一种特殊的方法创建对象。值得注意的是，根据MSXML解析器的不同版本，需要分别编写两种代码。

var xmlhttp = false;

try {

xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");

} catch (othermicrosoft) {

try {

xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

} catch (failed) {

xmlhttp = false;

}

因此，结合上述两个代码片段，我们得到了以下适合所有主流浏览器创建XMLHttpRequest对象的代码：

var xmlhttp = false;

try {

xmlhttp = new XMLHttpRequest();

} catch (trymicrosoft) {

try {

xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");

} catch (othermicrosoft) {

try {

xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

} catch (failed) {

xmlhttp = false;

}

}

}

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文章来自: Builder

标签: Ajax

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