📄 dom_httprequest.asp@output=print
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<title>XML DOM - HttpRequest object</title>
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
<h1> The XMLHttpRequest Object</h1>
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<p class="intro">The XMLHttpRequest object provides a way to communicate with a
server after a web page has loaded.</p>
<hr />
<h2>What is the XMLHttpRequest Object?</h2>
<p>The XMLHttpRequest object is <b>the developers dream</b>, because you can:</p>
<ul>
<li>Update a web page with new data without reloading the page</li>
<li>Request data from a server after the page has loaded </li>
<li>Receive data from a server after the page has loaded</li>
<li>Send data to a server in the background</li>
</ul>
<p>The XMLHttpRequest object is supported in all modern browsers.</p>
<p>Example:
<a target="_blank" href="tryit.asp@filename=try_dom_httpsuggest">XML
HTTP communication with a server while typing input</a></p>
<hr />
<h2>Creating an XMLHttpRequest Object</h2>
<p>Creating an XMLHttpRequest object is done with one single line of JavaScript.</p>
<p>In all modern browsers (including IE7):</p>
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<pre>xmlhttp=new XMLHttpRequest()</pre>
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<p>In Internet Explorer 5 and 6:</p>
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<pre>xmlhttp=new ActiveXObject("Microsoft.XMLHTTP")</pre>
</td>
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<h3>Example</h3>
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<pre><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.");
}
}</pre>
<pre>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></pre>
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<p><a target="_blank" href="tryit.asp@filename=try_dom_httprequest_js">Try it yourself using JavaScript</a></p>
<p><b>Note:</b> onreadystatechange is an event handler. The value (state_Change)
is the name of a function which is
triggered when the state of the XMLHttpRequest object changes. States run from 0 (uninitialized)
to 4 (complete). Only when the state = 4, we can execute our code.</p>
<hr />
<h2>Why Use Async=true?</h2>
<p>Our examples use "true" in the third parameter of open().</p>
<p>This parameter specifies
whether the request should be handled asynchronously.</p>
<p>True means
that the script
continues to run after the send() method, without waiting for a response
from the server.</p>
<p>The onreadystatechange event complicates the code. But it is the safest way
if you want to prevent the code from stopping if you don't get a response from
the server.</p>
<p>By setting the parameter to "false", your can avoid the extra
onreadystatechange code. Use this if it's not important to execute the rest of
the code if the request fails.</p>
<p><a target="_blank" href="tryit.asp@filename=try_dom_httprequest_js0">Try it yourself using JavaScript</a></p>
<hr />
<h2>More Examples</h2>
<p><a target="_blank" href="tryit.asp@filename=try_dom_httprequest_js1">Load a
textfile into a div element with XML HTTP</a></p>
<p><a target="_blank" href="tryit.asp@filename=try_dom_httprequest_js2">Make a
HEAD request with XML HTTP</a></p>
<p><a target="_blank" href="tryit.asp@filename=try_dom_httprequest_js3">Make a
specified HEAD request with XML HTTP</a></p>
<p><a target="_blank" href="tryit.asp@filename=try_dom_httprequest_js4">List data from an XML file with XML HTTP</a></p>
<hr />
<h2>XML / ASP</h2>
<p>You can also open and send an XML document to an ASP page on
the server, analyze the request, and send back the result.</p>
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<pre><html>
<body>
<script type="text/javascript">
xmlHttp=null;
if (window.XMLHttpRequest)
{// code for IE7, Firefox, Opera, etc.
xmlHttp=new XMLHttpRequest();
}
else if (window.ActiveXObject)
{// code for IE6, IE5
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
if (xmlHttp!=null)
{
xmlHttp.open("GET", "note.xml", false);
xmlHttp.send(null);
xmlDoc=xmlHttp.responseText;
xmlHttp.open("POST", "demo_dom_http.asp", false);
xmlHttp.send(xmlDoc);
document.write(xmlHttp.responseText);
}
else
{
alert("Your browser does not support XMLHTTP.");
}
</script>
</body>
</html></pre>
</td>
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<p>The ASP page, written in VBScript:</p>
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<td>
<pre><%
set xmldoc = Server.CreateObject("Microsoft.XMLDOM")
xmldoc.async=false
xmldoc.load(request)
for each x in xmldoc.documentElement.childNodes
if x.NodeName = "to" then name=x.text
next
response.write(name)
%></pre>
</td>
</tr>
</table>
<p>You send the result back to the client using the response.write property.</p>
<p><a target="_blank" href="tryit.asp@filename=try_dom_httpsend2">Try it yourself</a></p>
<hr />
<h2>Is the XMLHttpRequest Object a W3C Standard?</h2>
<p>The XMLHttpRequest object is not specified in any W3C
recommendation.</p>
<p>However, the W3C DOM Level 3 "Load and Save" specification contains some
similar functionality, but these are not implemented in any browsers yet.<br />
</p>
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
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