Develop Reference

Getting A Cross-Origin XmlHttpRequest to Return an XML File in HTML5

EDIT: REMEMBER TO ALWAYS CHECK YOUR NETWORK TAB FOR ERRORS, MY POSTED ANSWER ELABORATES THAT THIS WAS A STUPID QUESTION ON MY PART, THANKS epascarello
I'm writing some backend code for an HTML5 website and I can't get this very important function to work. The site will often need to dynamically pull PHP-generated XML files from a different server. I'm pretty sure that server has Access-Control-Allow-Origin set to allow requests from this server. I will verify with my boss but he's out for a couple days and honestly it's more likely something I'm doing wrong. Does anyone see something wrong with this code?
Notice I have an alert at the bottom before request.send(null) and after. .send() works fine and the function completes if I request an XML file from the same server, but if I request from the other I get the "before" alert but not the "after". I am also seeing no errors or other alerts displayed to me.
Notes:
There are some references to global variables and such in other .js files. I've determined that including them would be pointless and just clutter the question.
'cross' is just a boolean for whether the request is cross origin, to another server.
function createXmlHttpRequestObject(cross) {
if(cross === undefined) {
cross = false;
}
var xmlHttp;
if(cross) {
if(window.XDomainRequest) {
try {
xmlHttp = new window.XDomainRequest();
} catch(e) {
xmlHttp = false;
}
} else {
xmlHttp = new XMLHttpRequest();
}
} else {
if(window.ActiveXObject) {
try {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch(e) {
xmlHttp = false;
}
} else {
try {
xmlHttp = new XMLHttpRequest();
} catch(e) {
xmlHttp = false;
}
}
}
if(!xmlHttp) {
alert ("Error: CREATING XMLHTTP REQUEST OBJECT FAILED");
} else {
return xmlHttp;
}
}
//receives xml object from file
function getXmlObject(URL) {
//if url contains any of site root, then it is not cross domain
var cross = false;
if(!URL.includes(url_home)) {
cross = true;
}
var request = createXmlHttpRequestObject(cross);
var response;
if(window.ActiveXObject || window.XDomainRequest) {
request.onload = function(){
response = request.responseXML;
};
request.open('GET',URL,false);
request.send(null);
} else {
request.open('GET',URL,false);
request.onreadystatechange = function(){
if(request.readyState == 4) {
if(request.status == 200) {
response = request.responseXML;
} else {
var warn = 'NOT FOUND\n' + URL;
response = warn;
alert(warn);
}
}
};
alert("before");
request.send(null);
alert("after");
}
return response;
}

Found in the network tab confirmation that there is in fact no Access-Control-Allow-Origin flag on the server I'm trying to access. I'm gonna have to talk to the right people and see if that can change. Still, if this code can be improved or if there's still an issue here I'm not seeing please point it out.

phonegap + iOS, http request always return status 0 on local files

I am using Phonegap 3.3.0 and on iOS, the following http request always returns 0, whether the file exists or not !!
var url = './images/pros/imagefile.png';
var http = new XMLHttpRequest();
http.open('HEAD', url, false);
http.send();
http.status
It returns 0 if the file exists, but if I try a fake wrong url :
var url = 'httpbabla/images/pros/imagefile.pngfkjdqmkfjdmqsl';
or
var url = 'www/images/pros/imagefidddddddle.pngooijijijiojs';
it still returns 0.
Is it a phonegap bug ? If not, then how to quickly distinguish existing local files from unexisting files with Phonegap and iOS?
Thanks

You might have better luck with an asynchronous request and onload and onerror handlers. Note the use of a true parameter as the last argument to http.open:
var url = 'file:///does/not/exist.jpg';
var http = new XMLHttpRequest();
http.open('HEAD', url, true);
http.onload = function(e){/* Success! File exists; process the response... */};
http.onerror = function(e){/* Failed - file does not exist - do whatever needs to be done... */};
http.send();
Once you call http.send your function will be done and control will return to the caller. Whatever processing you need to do on either success or failure will need to be taken care of in the onload and onerror callbacks. Take the time to learn how to use Javascript callbacks (and closures) if you're not familiar with them - they're one of the most powerful features in the language.

This works for me :
function UrlExists(url)
{
if ( isPhoneGap && isIOS() ) {
if (url.fileExists()){ //see prototype below
return true;
}else {
return false;
}
} else {
try {
http = new XMLHttpRequest();
http.open("HEAD", url, false);
http.send();
}
catch (err) {
//alert("An error:" + err.name + "---" + err.message);
}
//return http.status!=404;
if (http.readyState == 4) {
console.log("http.status="+http.status);
return http.status==200 || http.status==0;
}
}
}
// check local file existance for iOS
String.prototype.fileExists = function() {
filename = this.trim();
var response = jQuery.ajax({
url: filename,
type: 'HEAD',
async: false
}).status;
return (response != "200") ? false : true;
}

How do I check if file exists in jQuery or pure JavaScript?

How do I check if a file on my server exists in jQuery or pure JavaScript?

With jQuery:
$.ajax({
url:'http://www.example.com/somefile.ext',
type:'HEAD',
error: function()
{
//file not exists
},
success: function()
{
//file exists
}
});
EDIT:
Here is the code for checking 404 status, without using jQuery
function UrlExists(url)
{
var http = new XMLHttpRequest();
http.open('HEAD', url, false);
http.send();
return http.status!=404;
}
Small changes and it could check for status HTTP status code 200 (success), instead.
EDIT 2: Since sync XMLHttpRequest is deprecated, you can add a utility method like this to do it async:
function executeIfFileExist(src, callback) {
var xhr = new XMLHttpRequest()
xhr.onreadystatechange = function() {
if (this.readyState === this.DONE) {
callback()
}
}
xhr.open('HEAD', src)
}

A similar and more up-to-date approach.
$.get(url)
.done(function() {
// exists code
}).fail(function() {
// not exists code
})

This works for me:
function ImageExist(url)
{
var img = new Image();
img.src = url;
return img.height != 0;
}

i used this script to add alternative image
function imgError()
{
alert('The image could not be loaded.');
}
HTML:
<img src="image.gif" onerror="imgError()" />
http://wap.w3schools.com/jsref/event_onerror.asp

So long as you're testing files on the same domain this should work:
function fileExists(url) {
if(url){
var req = new XMLHttpRequest();
req.open('GET', url, false);
req.send();
return req.status==200;
} else {
return false;
}
}
Please note, this example is using a GET request, which besides getting the headers (all you need to check weather the file exists) gets the whole file.
If the file is big enough this method can take a while to complete.
The better way to do this would be changing this line: req.open('GET', url, false); to req.open('HEAD', url, false);

Here's how to do it ES7 way, if you're using Babel transpiler or Typescript 2:
async function isUrlFound(url) {
try {
const response = await fetch(url, {
method: 'HEAD',
cache: 'no-cache'
});
return response.status === 200;
} catch(error) {
// console.log(error);
return false;
}
}
Then inside your other async scope, you can easily check whether url exist:
const isValidUrl = await isUrlFound('http://www.example.com/somefile.ext');
console.log(isValidUrl); // true || false

I was getting a cross domain permissions issue when trying to run the answer to this question so I went with:
function UrlExists(url) {
$('<img src="'+ url +'">').load(function() {
return true;
}).bind('error', function() {
return false;
});
}
It seems to work great, hope this helps someone!

All the other answers can fail due to cache!
Making a HTTP request to a file on server can be intercepted with HTTP cache and the cached response is then returned. But the file may be deleted on the server in the meantime, so ignoring cache may return false positive results.
Proper solution would be to create non-cached HTTP HEAD request. Nik Sumeiko's answer uses no-cache header which means that the response can be cached, but must be revalidated before reuse. In this case the server may return 304: Not Modified, which is not 200: OK and thus false negative.
To avoid cache, the correct header is Cache-Control: no-store
File can exist without HTTP 200 response
You should also keep in mind that redirection (301: Moved Permanently, 307: Temporary Redirect or 308: Permanent Redirect) may occur, so the file can exist elsewhere and may be returned from different location: depending on the use-case, one may choose to follow redirection instead of returning false in this case.
Also keep in mind that background requests will be blocked if you check file existence on different domain and its CORS policy is not opened to your server. In this case 403: Forbidden is usually returned, which doesn't mean file does not exist but file is unavailable. Last but not least, the same applies to 500: Internal Server Error response, which means that the HTTP server failed to handle the request, but the file can be available otherwise, like by FTP.
The following code will return true if the file exists, false if not or undefined if the file is unavailable or redirected:
const fileExists = file =>
fetch(file, {method: 'HEAD', cache: 'no-store'})
.then(response => ({200: true, 404: false})[response.status])
.catch(exception => undefined);
fileExists("yourFile.html").then(yes => yes && alert("yourFile.html exists"));
// or in the async scope...
let yourFileExists = await fileExists("yourFile.html");
if(yourFileExists) console.log("It is there!")
else if(yourFileExists===false) console.log("Nope, it was deleted.");
else console.log("You are not worthy the answer, puny human!");
Modern and obsolete approaches
Since we live in the future now, I would also recommend:
$.ajax() obsolete, don't use in new projects
XMLHttpRequest() obsolete, don't use in new projects
fetch() modern approach, use it if you are free to choose
Note GET/POST methods (like <img src...>) are not appropriate here as they waste network traffic by downloading the file (imagine the worst scenario with high resolution photo and user with paid mobile data in area with poor connectivity)
Note Modern PWA approach is to use Cache API with serviceWorker's fetch event which intercepts the communication between the client and HTTP cache. In the example in the link, there should be something like
if(event.request.cache=="no-store") {
// avoid cache storage and pass the request in the chain
// client - cache storage - HTTP cache - server
return fetch(event.request);
}
Without this, the cache settings may be ignored and there may be no way to detect the remote file existence from the main thread with the serviceWorker running - illustrated
here.

JavaScript function to check if a file exists:
function doesFileExist(urlToFile)
{
var xhr = new XMLHttpRequest();
xhr.open('HEAD', urlToFile, false);
xhr.send();
if (xhr.status == "404") {
console.log("File doesn't exist");
return false;
} else {
console.log("File exists");
return true;
}
}

I use this script to check if a file exists (also it handles the cross origin issue):
$.ajax(url, {
method: 'GET',
dataType: 'jsonp'
})
.done(function(response) {
// exists code
}).fail(function(response) {
// doesnt exist
})
Note that the following syntax error is thrown when the file being checked doesn't contain JSON.
Uncaught SyntaxError: Unexpected token <

For a client computer this can be achieved by:
try
{
var myObject, f;
myObject = new ActiveXObject("Scripting.FileSystemObject");
f = myObject.GetFile("C:\\img.txt");
f.Move("E:\\jarvis\\Images\\");
}
catch(err)
{
alert("file does not exist")
}
This is my program to transfer a file to a specific location and shows alert if it does not exist

An async call to see if a file exists is the better approach, because it doesn't degrade the user experience by waiting for a response from the server. If you make a call to .open with the third parameter set to false (as in many examples above, for example http.open('HEAD', url, false); ), this is a synchronous call, and you get a warning in the browser console.
A better approach is:
function fetchStatus( address ) {
var client = new XMLHttpRequest();
client.onload = function() {
// in case of network errors this might not give reliable results
returnStatus( this.status );
}
client.open( "HEAD", address, true );
client.send();
}
function returnStatus( status ) {
if ( status === 200 ) {
console.log( 'file exists!' );
}
else {
console.log( 'file does not exist! status: ' + status );
}
}
source: https://xhr.spec.whatwg.org/

This is an adaptation to the accepted answer, but I couldn't get what I needed from the answer, and had to test this worked as it was a hunch, so i'm putting my solution up here.
We needed to verify a local file existed, and only allow the file (a PDF) to open if it existed. If you omit the URL of the website, the browser will automatically determine the host name - making it work in localhost and on the server:
$.ajax({
url: 'YourFolderOnWebsite/' + SomeDynamicVariable + '.pdf',
type: 'HEAD',
error: function () {
//file not exists
alert('PDF does not exist');
},
success: function () {
//file exists
window.open('YourFolderOnWebsite/' + SomeDynamicVariable + '.pdf', "_blank", "fullscreen=yes");
}
});

First creates the function
$.UrlExists = function(url) {
var http = new XMLHttpRequest();
http.open('HEAD', url, false);
http.send();
return http.status!=404;
}
After using the function as follows
if($.UrlExists("urlimg")){
foto = "img1.jpg";
}else{
foto = "img2.jpg";
}
$('<img>').attr('src',foto);

Here's my working Async Pure Javascript from 2020
function testFileExists(src, successFunc, failFunc) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (this.readyState === this.DONE) {
if (xhr.status === 200) {
successFunc(xhr);
} else {
failFunc(xhr);
}
}
}
// xhr.error = function() {
// failFunc(xhr);
// }
// xhr.onabort = function() {
// failFunc(xhr);
// }
// xhr.timeout = function() {
// failFunc(xhr);
// }
xhr.timeout = 5000; // TIMEOUT SET TO PREFERENCE (5 SEC)
xhr.open('HEAD', src, true);
xhr.send(null); // VERY IMPORTANT
}
function fileExists(xhr) {
alert("File exists !! Yay !!");
}
function fileNotFound(xhr) {
alert("Cannot find the file, bummer");
}
testFileExists("test.html", fileExists, fileNotFound);
I could not force it to come back with any of the abort, error, or timeout callbacks.
Each one of these returned a main status code of 0, in the test above, so
I removed them. You can experiment.
I set the timeout to 5 seconds as the default seems to be very excessive.
With the Async call, it doesn't seem to do anything without the send() command.

What you'd have to do is send a request to the server for it to do the check, and then send back the result to you.
What type of server are you trying to communicate with? You may need to write a small service to respond to the request.

This doesn't address the OP's question, but for anyone who is returning results from a database: here's a simple method I used.
If the user didn't upload an avatar the avatar field would be NULL, so I'd insert a default avatar image from the img directory.
function getAvatar(avatar) {
if(avatar == null) {
return '/img/avatar.jpg';
} else {
return '/avi/' + avatar;
}
}
then
<img src="' + getAvatar(data.user.avatar) + '" alt="">

It works for me, use iframe to ignore browsers show GET error message
var imgFrame = $('<iframe><img src="' + path + '" /></iframe>');
if ($(imgFrame).find('img').attr('width') > 0) {
// do something
} else {
// do something
}

I wanted a function that would return a boolean, I encountered problems related to closure and asynchronicity. I solved this way:
checkFileExistence= function (file){
result=false;
jQuery.ajaxSetup({async:false});
$.get(file)
.done(function() {
result=true;
})
.fail(function() {
result=false;
})
jQuery.ajaxSetup({async:true});
return(result);
},

How do I make Ajax calls at intervals without overlap?

I'm looking to setup a web page that samples data via AJAX calls from an embedded web-server. How would I set up the code so that one request doesn't overlap another?
I should mention I have very little JavaScript experience and also a compelling reason not to use external libraries of any size bigger than maybe 10 or so kilobytes.

You may want to consider the option of relaunching your AJAX request ONLY after a successful response from the previous AJAX call.
function autoUpdate()
{
var ajaxConnection = new Ext.data.Connection();
ajaxConnection.request(
{
method: 'GET',
url: '/web-service/',
success: function(response)
{
// Add your logic here for a successful AJAX response.
// ...
// ...
// Relaunch the autoUpdate() function in 5 seconds.
setTimeout(autoUpdate, 5000);
}
}
}
This example uses ExtJS, but you could very easily use just XMLHttpRequest.
NOTE: If you must have an exact interval of x seconds, you would have to keep track of the time passed from when the AJAX request was launched up to the setTimeout() call, and then subtract this timespan from the delay. Otherwise, the interval time in the above example will vary with the network latency and with the time to processes the web service logic.

I suggest you use a small toolkit like jx.js (source). You can find it here: http://www.openjs.com/scripts/jx/ (less than 1k minified)
To setup a request:
jx.load('somepage.php', function(data){
alert(data); // Do what you want with the 'data' variable.
});
To set it up on an interval you can use setInterval and a variable to store whether or not a request is currently occuring - if it is, we simple do nothing:
var activeRequest = false;
setInterval(function(){
if (!activeRequest) {
// Only runs if no request is currently occuring:
jx.load('somepage.php', function(data){
activeRequest = false;
alert(data); // Do what you want with the 'data' variable.
});
}
activeRequest = true;
}, 5000); // Every five seconds

AJAX, despite the name, need not be asynchronous.
Here is the asynchronous method...
var req;
function ajax(method,url,payload,action)
{
if (window.XMLHttpRequest)
{
req = new XMLHttpRequest();
req.onreadystatechange = action;
req.open(method, url, true);
req.send(payload);
}
else if (window.ActiveXObject)
{
req = new ActiveXObject("Microsoft.XMLHTTP");
if (req)
{
req.onreadystatechange = action;
req.open(method, url, true);
req.send(payload);
}
else
{
alert("Could not create ActiveXObject(Microsoft.XMLHTTP)");
}
}
}
...but here is a synchronous equivalent...
function sjax(method,url,payload,action)
{
if (window.XMLHttpRequest)
{
req = new XMLHttpRequest();
req.open(method, url, false);
req.send(payload);
action();
}
else if (window.ActiveXObject)
{
req = new ActiveXObject("Microsoft.XMLHTTP");
if (req)
{
req.onreadystatechange = action;
req.open(method, url, false);
req.send(payload);
}
else
{
alert("Could not create ActiveXObject(Microsoft.XMLHTTP)");
}
}
}
... and here is a typical action ...
function insertHtml(target)
{
var pageTarget = arguments[0];
if (req.readyState == 4) // 4 == "loaded"
{
if (req.status == 200) // 200 == "Ok"
{
if (req.responseText.indexOf("error") >= 0)
{
alert("Please report the following error...");
pretty = req.responseText.substring(req.responseText.indexOf("error"),1200);
pretty = pretty.substring(0,pretty.indexOf("\""));
alert(pretty + "\n\n" + req.responseText.substring(0,1200));
}
else
{
div = document.getElementById(pageTarget);
div.innerHTML = req.responseText;
dimOff();
}
}
else
{
alert("Could not retreive URL:\n" + req.statusText);
}
}
}

AJAX responseXML errors

I've been having some weird issues when it comes to make an AJAX request and handling the response.
I am making an ajax call for an xml file. however when i get the response the xhr.responseText property works fine in firefox but not in IE.
Another thing is that I am trying to access the xhr.responseXML as XMLDocument, but it tells me in firefox it tells me that xhr.responseXML is undefined in ie it doesnt even show me the undefined error or displays the output.
This is the code I am using to make the request:
var ajaxReq = function(url, callback) {
//initialize the xhr object and settings
var xhr = window.ActiveXObject ?
new ActiveXObject("Microsoft.XMLHTTP") : new XMLHttpRequest(),
//set the successful connection function
httpSuccess = function(xhr) {
try {
// IE error sometimes returns 1223 when it should be 204
// so treat it as success, see XMLHTTPRequest #1450
// this code is taken from the jQuery library with some modification.
return !xhr.status && xhr.status == 0 ||
(xhr.status >= 200 && xhr.status < 300) ||
xhr.status == 304 || xhr.status == 1223;
} catch (e) { }
return false;
};
//making sure the request is created
if (!xhr) {
return 404; // Not Found
}
//setting the function that is going to be called after the request is made
xhr.onreadystatechange = function() {
if (!httpSuccess(xhr)) {
return 503; //Service Unavailable
}
if (xhr.responseXML != null && xhr.responseText != null &&
xhr.responseXML != undefined && xhr.responseText != undefined) {
callback(xhr);
}
};
//open request call
xhr.open('GET', url, true);
//setup the headers
try {
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.setRequestHeader("Accept", "text/xml, application/xml, text/plain");
} catch ( ex ) {
window.alert('error' + ex.toString());
}
//send the request
try {
xhr.send('');
} catch (e) {
return 400; //bad request
}
return xhr;
};
and this is how i am calling the function to test for results:
window.onload = function() {
ajaxReq('ConferenceRoomSchedules.xml', function(xhr) {
//in firefox this line works fine,
//but in ie it doesnt not even showing an error
window.document.getElementById('schedule').innerHTML = xhr.responseText;
//firefox says ''xhr.responseXML is undefined'.
//and ie doesn't even show error or even alerts it.
window.alert(xhr.reponseXML.documentElement.nodeName);
});
}
This is also my first attempt to work with AJAX so there might be something that I am not looking at right.
I've been searching crazy for any indications of why or how to fix it, but no luck there.
any ideas would be great.
EDIT:
I know this would be better with a framework, but the boss doesn't want to add a framework for just an ajax functionality ('just' is not a fair word for ajax :P). So I am doing it with pure javascript.
The XML file is well-formed, I see it well in the web browser, but for completion this is the testing file I am using:
<?xml version="1.0" encoding="utf-8"?>
<rooms>
<room id="Blue_Room">
<administrator>somebody#department</administrator>
<schedule>
<event>
<requester>
<name>Johnny Bravo</name>
<email>jbravo#department</email>
</requester>
<date>2009/09/03</date>
<start_time>11:00:00 GMT-0600</start_time>
<end_time>12:00:00 GMT-0600</end_time>
</event>
</schedule>
</room>
<room id="Red_Room">
<administrator>somebody#department</administrator>
<schedule>
</schedule>
</room>
<room id="Yellow_Room">
<administrator>somebody#department</administrator>
<schedule>
</schedule>
</room>
</rooms>
EDIT 2:
Well the good news is that I convinced my boss to use jQuery, the bad news is that AJAX still perplexes me. I'll read more about it just for curiousity. Thanks for the tips and I gave the answer credit to Heat Miser because he was the closest working tip.

I was having the same problem a few years ago, then I gave up on responseXML and began always using responseText. This parsing function has always worked for me:
function parseXml(xmlText){
try{
var text = xmlText;
//text = replaceAll(text,"<","<");
//text = replaceAll(text,">",">");
//text = replaceAll(text,""","\"");
//alert(text);
//var myWin = window.open('','win','resize=yes,scrollbars=yes');
//myWin.document.getElementsByTagName('body')[0].innerHTML = text;
if (typeof DOMParser != "undefined") {
// Mozilla, Firefox, and related browsers
var parser=new DOMParser();
var doc=parser.parseFromString(text,"text/xml");
//alert(text);
return doc;
}else if (typeof ActiveXObject != "undefined") {
// Internet Explorer.
var doc = new ActiveXObject("Microsoft.XMLDOM"); // Create an empty document
doc.loadXML(text); // Parse text into it
return doc; // Return it
}else{
// As a last resort, try loading the document from a data: URL
// This is supposed to work in Safari. Thanks to Manos Batsis and
// his Sarissa library (sarissa.sourceforge.net) for this technique.
var url = "data:text/xml;charset=utf-8," + encodeURIComponent(text);
var request = new XMLHttpRequest();
request.open("GET", url, false);
request.send(null);
return request.responseXML;
}
}catch(err){
alert("There was a problem parsing the xml:\n" + err.message);
}
}
With this XMLHttpRequest Object:
// The XMLHttpRequest class object
debug = false;
function Request (url,oFunction,type) {
this.funct = "";
// this.req = "";
this.url = url;
this.oFunction = oFunction;
this.type = type;
this.doXmlhttp = doXmlhttp;
this.loadXMLDoc = loadXMLDoc;
}
function doXmlhttp() {
//var funct = "";
if (this.type == 'text') {
this.funct = this.oFunction + '(req.responseText)';
} else {
this.funct = this.oFunction + '(req.responseXML)';
}
this.loadXMLDoc();
return false;
}
function loadXMLDoc() {
//alert(url);
var functionA = this.funct;
var req;
req = false;
function processReqChange() {
// alert('reqChange is being called');
// only if req shows "loaded"
if (req.readyState == 4) {
// only if "OK"
if (req.status == 200) {
// ...processing statements go here...
eval(functionA);
if(debug){
var debugWin = window.open('','aWindow','width=600,height=600,scrollbars=yes');
debugWin.document.body.innerHTML = req.responseText;
}
} else {
alert("There was a problem retrieving the data:\n" +
req.statusText + '\nstatus: ' + req.status);
if(debug){
var debugWin = window.open('','aWindow','width=600,height=600,scrollbars=yes');
debugWin.document.body.innerHTML = req.responseText;
}
}
}
}
// branch for native XMLHttpRequest object
if(window.XMLHttpRequest) {
try {
req = new XMLHttpRequest();
} catch(e) {
req = false;
}
// branch for IE/Windows ActiveX version
} else if(window.ActiveXObject) {
try {
req = new ActiveXObject("Msxml2.XMLHTTP");
} catch(e) {
try {
req = new ActiveXObject("Microsoft.XMLHTTP");
} catch(e) {
req = false;
}
}
}
if(req) {
req.onreadystatechange = processReqChange;
if(this.url.length > 2000){
var urlSpl = this.url.split('?');
req.open("POST",urlSpl[0],true);
req.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
req.send(urlSpl[1]);
} else {
req.open("GET", this.url, true);
req.send("");
}
}
}
function browserSniffer(){
if(navigator.userAgent.toLowerCase().indexOf("msie") != -1){
if(navigator.userAgent.toLowerCase().indexOf("6")){
return 8;
}else{
return 1;
}
}
if(navigator.userAgent.toLowerCase().indexOf("firefox") != -1){
return 2;
}
if(navigator.userAgent.toLowerCase().indexOf("opera") != -1){
return 3;
}
if(navigator.userAgent.toLowerCase().indexOf("safari") != -1){
return 4;
}
return 5;
}
Granted, this is very old code, but it is still working for me on a site I built a few years ago. I agree with everyone else though I typically use a framework nowadays so I don't have to use this code or anything like it anymore.
You can ignore some of the particulars with the split, etc... in the Request onreadystate function. It was supposed to convert the request to a post if it was longer than a certain length, but I just decided it was always better to do a post.

This problem occurs mostly when content type is mis-detected by the browser or it's not sent correctly.
Its easier to just override it:
var request = new XMLHttpRequest();
request.open("GET", url, false);
request.overrideMimeType("text/xml");
request.send(null);
return request.responseXML;
Not sure why... This problem occurs only with Safari and Chrome (WebKit browsers, the server sends the headers correctly).

Are you calling the URL relative to the current document? Since IE would be using the ActiveXObject, it might need an absolute path, for example:
http://some.url/ConferenceRoomSchedules.xml
As for the XML, are you sure it's well-formed? Does it load in an XML editor, for instance?

What I can suggest you is to take a look at frameworks that hide and manage these cross-browser issues for you (in a reliable way). A good point here is jQuery. Doing these things yourself can become quite difficult and complex.
This may be what you need.
//Edit:
This is how the w3school shows it:
function ajaxFunction()
{
var xmlhttp;
if (window.XMLHttpRequest)
{
// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else if (window.ActiveXObject)
{
// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
else
{
alert("Your browser does not support XMLHTTP!");
}
}

To avoid your cross browser problems (and save yourself coding a lot of items that a strong community has already developed, tested, and reviewed), you should select a javascript library. JQuery and Dojo are great choices.

I believe that your web server need to serve correct response headers with 'ConferenceRoomSchedules.xml' e.g. Content-Type: text/xml or any other xml type.

The answer provided by Aron in https://stackoverflow.com/a/2081466/657416 is from my point of view the simplest (and the best) one. Here is my working code:
ajax = ajaxRequest();
ajax.overrideMimeType("text/xml");
ajax.open("GET", myurl;