↑
Main Page

createXMLHTTP

with the HTTP status of the request (200 is good, 404 means the page wasn’t found, and so on). It also

fills the

statusText

property with a message describing the status and the

responseText

property

with the text received back from the server. Additionally, if the text is XML, it fills the

responseXML

property, which is an XML DOM object constructed from the returned text. For example:

var oRequest = createXMLHTTP();

oRequest.open(“get”, “example.txt”, false);

oRequest.send(null);

alert(“Status is “ + oRequest.status + “ (“ + oRequest.statusText + “)”);

alert(“Response text is: “ + oRequest.responseText);

This example gets a plain text file and displays its contents. The

status

and

statusText

are also

displayed.

Requesting an XML file also fills the

responseXML

property:

var oRequest = createXMLHTTP();

oRequest.open(“get”, “example.xml”, false);

oRequest.send(null);

alert(“Status is “ + oRequest.status + “ (“ + oRequest.statusText + “)”);

alert(“Response text is: “ + oRequest.responseText);

alert(“Tag name of document element is: “ +

oRequest.responseXML.documentElement.tagname);

This example shows the tag name of the document element loaded into the

responseXML

property.

If you decide to send an asynchronous request, you must use the

onreadystatechange

event handler

to see when the

readyState

property is equal to

(the same as with the XML DOM). All the same

properties and methods are used, with the slight alteration that the response properties can’t be used

until the request has completed:

var oRequest = createXMLHTTP();

oRequest.open(“get”, “example.txt”, true);

oRequest.onreadystatechange = function () {

if (oRequest.readyState == 4) {

alert(“Status is “ + oRequest.status + “ (“ + oRequest.statusText + “)”);

alert(“Response text is: “ + oRequest.responseText);

}

oRequest.send(null);

This example doesn’t work when run locally: It must be run on a server because the

XML HTTP object relies on the server-reported mime type to determine if the

requested file is an XML document.

If you run this example locally, the

status

and the

statusText

“Unknown”

because a local file read isn’t an actual HTTP request.

494

Chapter 16

19_579088 ch16.qxd 3/28/05 11:42 AM Page 494