XMLHttpRequest对象是什么
XMLHttpRequest是一个API对象,用于在后台与服务器交换数据;所有现代的浏览器都支持XMLHttpRequest对象,创建XMLHttpRequest对象的语法是“xmlhttp=new XMLHttpRequest();”。
XMLHttpRequest对象是什么?
XMLHttpRequest(XHR)是一个API对象,其中的方法可以用来在浏览器和服务器端传输数据。这个对象是浏览器的js环境提供的。从XHR获取数据的目的是为了持续修改一个加载过的页面,XHR是Ajax设计的底层概念。XHR使用的协议不同于HTTP,不仅可以使用XML格式的数据,也支持JSON,HTML或者纯文本。
XMLHttpRequest 对象用于在后台与服务器交换数据。
XMLHttpRequest 对象是开发者的梦想,因为您能够:
在不重新加载页面的情况下更新网页
在页面已加载后从服务器请求数据
在页面已加载后从服务器接收数据
在后台向服务器发送数据
所有现代的浏览器都支持 XMLHttpRequest 对象。
如需学习更多有关 XMLHttpRequest 对象的知识,请学习我们的 XML DOM 教程。
实例:当键入文本时与服务器进行 XML HTTP 通信。
创建 XMLHttpRequest 对象
所有现代浏览器 (IE7+、Firefox、Chrome、Safari 以及 Opera) 都内建了 XMLHttpRequest 对象。
通过一行简单的 JavaScript 代码,我们就可以创建 XMLHttpRequest 对象。
创建 XMLHttpRequest 对象的语法:
xmlhttp=new XMLHttpRequest();
老版本的 Internet Explorer (IE5 和 IE6)使用 ActiveX 对象:
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
提示:在下一章,我们将使用 XMLHttpRequest 对象从服务器取回 XML 信息。
实例
<script type="text/javascript"> var xmlhttp; function loadXMLDoc(url) { xmlhttp=null; if (window.XMLHttpRequest) {// code for all new browsers xmlhttp=new XMLHttpRequest(); } else if (window.ActiveXObject) {// code for IE5 and IE6 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } if (xmlhttp!=null) { xmlhttp.onreadystatechange=state_Change; xmlhttp.open("GET",url,true); xmlhttp.send(null); } else { alert("Your browser does not support XMLHTTP."); } } function state_Change() { if (xmlhttp.readyState==4) {// 4 = "loaded" if (xmlhttp.status==200) {// 200 = OK // ...our code here... } else { alert("Problem retrieving XML data"); } } } </script>
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