使用 JavaScript 实现 XMLHttpRequest

2008-02-23 07:46:15来源：互联网阅读 ()

XMLHttp 方式实现无刷屏,在IE,FireFox 上测试通过

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/tr/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<style>
html {background-color:#eeeeee}
body {
background-color:#ccffcc;
font-family:Tahoma,Arial,Helvetica,sans-serif;
font-size:12px;
margin-left:15%;
margin-right:15%;
border:3px groove #006600;
padding:15px
}
h1 {
text-align:left;
font-size:1.5em;
font-weight:bold
}
</style>
<script type="text/javascript">
// global flag
var isIE = false;

// global request and XML document objects
var req;

// retrieve XML document (reusable generic function);
// parameter is URL string (relative or complete) to
// an .xml file whose Content-Type is a valid XML
// type, such as text/xml; XML source must be from
// same domain as HTML file
function loadXMLDoc(url) {
// branch for native XMLHttpRequest object
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
req.onreadystatechange = processReqChange;
req.open("GET", url, true);
req.send(null);
// branch for IE/Windows ActiveX version
} else if (window.ActiveXObject) {
isIE = true;
req = new ActiveXObject("Microsoft.XMLHTTP");
if (req) {
req.onreadystatechange = processReqChange;
req.open("GET", url, true);
req.send();
}
}
}

// handle onreadystatechange event of req object
function processReqChange() {
// only if req shows "loaded"
if (req.readyState == 4) {
// only if "OK"
if (req.status == 200) {
clearTopicList();
buildTopicList();
} else {
alert("There was a problem retrieving the XML data:\n"
req.statusText);
}
}
}

// invoked by "Category" select element change;
// loads chosen XML document, clears Topics select
// element, loads new items into Topics select element
function loadDoc(evt) {
// equalize W3C/IE event models to get event object
evt = (evt) ? evt : ((window.event) ? window.event : null);
if (evt) {
// equalize W3C/IE models to get event target reference
var elem = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);
if (elem) {
try {
if (elem.selectedIndex > 0) {
loadXMLDoc(elem.options[elem.selectedIndex].value);
}
}
catch(e) {
var msg = (typeof e == "string") ? e : ((e.message) ? e.message : "Unknown Error");
alert("Unable to get XML data:\n" msg);
return;
}
}
}
}

// retrieve text of an XML document element, including
// elements using namespaces
function getElementTextNS(prefix, local, parentElem, index) {
var result = "";
if (prefix && isIE) {
// IE/Windows way of handling namespaces
result = parentElem.getElementsByTagName(prefix ":" local)[index];
} else {
// the namespace versions of this method
// (getElementsByTagNameNS()) operate
// differently in Safari and Mozilla, but both
// return value with just local name, provided
// there aren't conflicts with non-namespace element
// names
result = parentElem.getElementsByTagName(local)[index];
}
if (result) {
// get text, accounting for possible
// whitespace (carriage return) text nodes
if (result.childNodes.length > 1) {
return result.childNodes[1].nodeValue;
} else {
return result.firstChild.nodeValue;
}
} else {
return "n/a";
}
}

// empty Topics select list content
function clearTopicList() {
var select = document.getElementById("topics");
while (select.length > 0) {
select.remove(0);
}
}

// add item to select element the less
// elegant, but compatible way.
function appendToSelect(select, value, content) {
var opt;
opt = document.createElement("option");
opt.value = value;
opt.appendChild(content);
select.appendChild(opt);
}

// fill Topics select list with items from
// the current XML document
function buildTopicList() {
var select = document.getElementById("topics");
var items = req.responseXML.getElementsByTagName("item");
// loop through <item> elements, and add each nested
// <title> element to Topics select element
for (var i = 0; i < items.length; i ) {
appendToSelect(select, i,

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