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How to get source code of specific URL in JavaScript? [duplicate]

I need to do an HTTP GET request in JavaScript. What's the best way to do that?
I need to do this in a Mac OS X dashcode widget.

Browsers (and Dashcode) provide an XMLHttpRequest object which can be used to make HTTP requests from JavaScript:
function httpGet(theUrl)
{
var xmlHttp = new XMLHttpRequest();
xmlHttp.open( "GET", theUrl, false ); // false for synchronous request
xmlHttp.send( null );
return xmlHttp.responseText;
}
However, synchronous requests are discouraged and will generate a warning along the lines of:
Note: Starting with Gecko 30.0 (Firefox 30.0 / Thunderbird 30.0 / SeaMonkey 2.27), synchronous requests on the main thread have been deprecated due to the negative effects to the user experience.
You should make an asynchronous request and handle the response inside an event handler.
function httpGetAsync(theUrl, callback)
{
var xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = function() {
if (xmlHttp.readyState == 4 && xmlHttp.status == 200)
callback(xmlHttp.responseText);
}
xmlHttp.open("GET", theUrl, true); // true for asynchronous
xmlHttp.send(null);
}

window.fetch is a modern replacement for XMLHttpRequest that makes use of ES6 promises. There's a nice explanation here, but it boils down to (from the article):
fetch(url).then(function(response) {
return response.json();
}).then(function(data) {
console.log(data);
}).catch(function(err) {
console.log('Fetch Error :-S', err);
});
Browser support has been good since 2017. IE will likely not get official support. GitHub has a polyfill available adds support to some legacy browsers (esp versions of Safari pre March 2017 and mobile browsers from the same period).
I guess whether this is more convenient than jQuery or XMLHttpRequest or not depends on the nature of the project.
Here's a link to the spec https://fetch.spec.whatwg.org/
Edit:
Using ES7 async/await, this becomes simply (based on this Gist):
async function fetchAsync (url) {
let response = await fetch(url);
let data = await response.json();
return data;
}

In jQuery:
$.get(
"somepage.php",
{paramOne : 1, paramX : 'abc'},
function(data) {
alert('page content: ' + data);
}
);

Lots of great advice above, but not very reusable, and too often filled with DOM nonsense and other fluff that hides the easy code.
Here's a Javascript class we created that's reusable and easy to use. Currently it only has a GET method, but that works for us. Adding a POST shouldn't tax anyone's skills.
var HttpClient = function() {
this.get = function(aUrl, aCallback) {
var anHttpRequest = new XMLHttpRequest();
anHttpRequest.onreadystatechange = function() {
if (anHttpRequest.readyState == 4 && anHttpRequest.status == 200)
aCallback(anHttpRequest.responseText);
}
anHttpRequest.open( "GET", aUrl, true );
anHttpRequest.send( null );
}
}
Using it is as easy as:
var client = new HttpClient();
client.get('http://some/thing?with=arguments', function(response) {
// do something with response
});

A version without callback
var i = document.createElement("img");
i.src = "/your/GET/url?params=here";

Here is code to do it directly with JavaScript. But, as previously mentioned, you'd be much better off with a JavaScript library. My favorite is jQuery.
In the case below, an ASPX page (that's servicing as a poor man's REST service) is being called to return a JavaScript JSON object.
var xmlHttp = null;
function GetCustomerInfo()
{
var CustomerNumber = document.getElementById( "TextBoxCustomerNumber" ).value;
var Url = "GetCustomerInfoAsJson.aspx?number=" + CustomerNumber;
xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = ProcessRequest;
xmlHttp.open( "GET", Url, true );
xmlHttp.send( null );
}
function ProcessRequest()
{
if ( xmlHttp.readyState == 4 && xmlHttp.status == 200 )
{
if ( xmlHttp.responseText == "Not found" )
{
document.getElementById( "TextBoxCustomerName" ).value = "Not found";
document.getElementById( "TextBoxCustomerAddress" ).value = "";
}
else
{
var info = eval ( "(" + xmlHttp.responseText + ")" );
// No parsing necessary with JSON!
document.getElementById( "TextBoxCustomerName" ).value = info.jsonData[ 0 ].cmname;
document.getElementById( "TextBoxCustomerAddress" ).value = info.jsonData[ 0 ].cmaddr1;
}
}
}

A copy-paste modern version ( using fetch and arrow function ) :
//Option with catch
fetch( textURL )
.then(async r=> console.log(await r.text()))
.catch(e=>console.error('Boo...' + e));
//No fear...
(async () =>
console.log(
(await (await fetch( jsonURL )).json())
)
)();
A copy-paste classic version:
let request = new XMLHttpRequest();
request.onreadystatechange = function () {
if (this.readyState === 4) {
if (this.status === 200) {
document.body.className = 'ok';
console.log(this.responseText);
} else if (this.response == null && this.status === 0) {
document.body.className = 'error offline';
console.log("The computer appears to be offline.");
} else {
document.body.className = 'error';
}
}
};
request.open("GET", url, true);
request.send(null);

Short and clean:
const http = new XMLHttpRequest()
http.open("GET", "https://api.lyrics.ovh/v1/toto/africa")
http.send()
http.onload = () => console.log(http.responseText)

IE will cache URLs in order to make loading faster, but if you're, say, polling a server at intervals trying to get new information, IE will cache that URL and will likely return the same data set you've always had.
Regardless of how you end up doing your GET request - vanilla JavaScript, Prototype, jQuery, etc - make sure that you put a mechanism in place to combat caching. In order to combat that, append a unique token to the end of the URL you're going to be hitting. This can be done by:
var sURL = '/your/url.html?' + (new Date()).getTime();
This will append a unique timestamp to the end of the URL and will prevent any caching from happening.

Modern, clean and shortest
fetch('https://baconipsum.com/api/?type=1')
let url = 'https://baconipsum.com/api/?type=all-meat&paras=1&start-with-lorem=2';
// to only send GET request without waiting for response just call
fetch(url);
// to wait for results use 'then'
fetch(url).then(r=> r.json().then(j=> console.log('\nREQUEST 2',j)));
// or async/await
(async()=>
console.log('\nREQUEST 3', await(await fetch(url)).json())
)();
Open Chrome console network tab to see request

Prototype makes it dead simple
new Ajax.Request( '/myurl', {
method: 'get',
parameters: { 'param1': 'value1'},
onSuccess: function(response){
alert(response.responseText);
},
onFailure: function(){
alert('ERROR');
}
});

One solution supporting older browsers:
function httpRequest() {
var ajax = null,
response = null,
self = this;
this.method = null;
this.url = null;
this.async = true;
this.data = null;
this.send = function() {
ajax.open(this.method, this.url, this.asnyc);
ajax.send(this.data);
};
if(window.XMLHttpRequest) {
ajax = new XMLHttpRequest();
}
else if(window.ActiveXObject) {
try {
ajax = new ActiveXObject("Msxml2.XMLHTTP.6.0");
}
catch(e) {
try {
ajax = new ActiveXObject("Msxml2.XMLHTTP.3.0");
}
catch(error) {
self.fail("not supported");
}
}
}
if(ajax == null) {
return false;
}
ajax.onreadystatechange = function() {
if(this.readyState == 4) {
if(this.status == 200) {
self.success(this.responseText);
}
else {
self.fail(this.status + " - " + this.statusText);
}
}
};
}
Maybe somewhat overkill but you definitely go safe with this code.
Usage:
//create request with its porperties
var request = new httpRequest();
request.method = "GET";
request.url = "https://example.com/api?parameter=value";
//create callback for success containing the response
request.success = function(response) {
console.log(response);
};
//and a fail callback containing the error
request.fail = function(error) {
console.log(error);
};
//and finally send it away
request.send();

To do this Fetch API is the recommended approach, using JavaScript Promises. XMLHttpRequest (XHR), IFrame object or dynamic <script> tags are older (and clunkier) approaches.
<script type=“text/javascript”>
// Create request object
var request = new Request('https://example.com/api/...',
{ method: 'POST',
body: {'name': 'Klaus'},
headers: new Headers({ 'Content-Type': 'application/json' })
});
// Now use it!
fetch(request)
.then(resp => {
// handle response
})
.catch(err => {
// handle errors
});
</script>
Here is a great fetch demo and MDN docs

I'm not familiar with Mac OS Dashcode Widgets, but if they let you use JavaScript libraries and support XMLHttpRequests, I'd use jQuery and do something like this:
var page_content;
$.get( "somepage.php", function(data){
page_content = data;
});

SET OF FUNCTIONS RECIPES EASY AND SIMPLE
I prepared a set of functions that are somehow similar but yet demonstrate new functionality as well as the simplicity that Javascript has reached if you know how to take advantage of it.
Let some basic constants
let data;
const URLAPI = "https://gorest.co.in/public/v1/users";
function setData(dt) {
data = dt;
}
Most simple
// MOST SIMPLE ONE
function makeRequest1() {
fetch(URLAPI)
.then(response => response.json()).then( json => setData(json))
.catch(error => console.error(error))
.finally(() => {
console.log("Data received 1 --> ", data);
data = null;
});
}
Variations using Promises and Async facilities
// ASYNC FUNCTIONS
function makeRequest2() {
fetch(URLAPI)
.then(async response => await response.json()).then(async json => await setData(json))
.catch(error => console.error(error))
.finally(() => {
console.log("Data received 2 --> ", data);
data = null;
});
}
function makeRequest3() {
fetch(URLAPI)
.then(async response => await response.json()).then(json => setData(json))
.catch(error => console.error(error))
.finally(() => {
console.log("Data received 3 --> ", data);
data = null;
});
}
// Better Promise usages
function makeRequest4() {
const response = Promise.resolve(fetch(URLAPI).then(response => response.json())).then(json => setData(json) ).finally(()=> {
console.log("Data received 4 --> ", data);
})
}
Demostration of one liner function!!!
// ONE LINER STRIKE ASYNC WRAPPER FUNCTION
async function makeRequest5() {
console.log("Data received 5 -->", await Promise.resolve(fetch(URLAPI).then(response => response.json().then(json => json ))) );
}
WORTH MENTION ---> #Daniel De León propably the cleanest function*
(async () =>
console.log(
(await (await fetch( URLAPI )).json())
)
)();
The top answer -> By #tggagne shows functionality with HttpClient API.
The same can be achieve with Fetch. As per this Using Fetch by MDN shows how you can pass a INIT as second argument, basically opening the possibility to configure easily an API with classic methods (get, post...) .
// Example POST method implementation:
async function postData(url = '', data = {}) {
// Default options are marked with *
const response = await fetch(url, {
method: 'POST', // *GET, POST, PUT, DELETE, etc.
mode: 'cors', // no-cors, *cors, same-origin
cache: 'no-cache', // *default, no-cache, reload, force-cache, only-if-cached
credentials: 'same-origin', // include, *same-origin, omit
headers: {
'Content-Type': 'application/json'
// 'Content-Type': 'application/x-www-form-urlencoded',
},
redirect: 'follow', // manual, *follow, error
referrerPolicy: 'no-referrer', // no-referrer, *no-referrer-when-downgrade, origin, origin-when-cross-origin, same-origin, strict-origin, strict-origin-when-cross-origin, unsafe-url
body: JSON.stringify(data) // body data type must match "Content-Type" header
});
return response.json(); // parses JSON response into native JavaScript objects
}
postData('https://example.com/answer', { answer: 42 })
.then(data => {
console.log(data); // JSON data parsed by `data.json()` call
});
Node
Fetch is not available on Node (Server Side)
The easiest solution (end of 2021) is to use Axios.
$ npm install axios
Then Run:
const axios = require('axios');
const request = async (url) => await (await axios.get( url ));
let response = request(URL).then(resp => console.log(resp.data));

In your widget's Info.plist file, don't forget to set your AllowNetworkAccess key to true.

For those who use AngularJs, it's $http.get:
$http.get('/someUrl').
success(function(data, status, headers, config) {
// this callback will be called asynchronously
// when the response is available
}).
error(function(data, status, headers, config) {
// called asynchronously if an error occurs
// or server returns response with an error status.
});

You can get an HTTP GET request in two ways:
This approach based on xml format. You have to pass the URL for the request.
xmlhttp.open("GET","URL",true);
xmlhttp.send();
This one is based on jQuery. You have to specify the URL and function_name you want to call.
$("btn").click(function() {
$.ajax({url: "demo_test.txt", success: function_name(result) {
$("#innerdiv").html(result);
}});
});

The best way is to use AJAX ( you can find a simple tutorial on this page Tizag). The reason is that any other technique you may use requires more code, it is not guaranteed to work cross browser without rework and requires you use more client memory by opening hidden pages inside frames passing urls parsing their data and closing them.
AJAX is the way to go in this situation. That my two years of javascript heavy development speaking.

now with asynchronus js we can use this method with fetch() method to make promises in a more concise way. Async functions are supported in all modern browsers.
async function funcName(url){
const response = await fetch(url);
var data = await response.json();
}

function get(path) {
var form = document.createElement("form");
form.setAttribute("method", "get");
form.setAttribute("action", path);
document.body.appendChild(form);
form.submit();
}
get('/my/url/')
Same thing can be done for post request as well.
Have a look at this link JavaScript post request like a form submit

To refresh best answer from joann with promise this is my code:
let httpRequestAsync = (method, url) => {
return new Promise(function (resolve, reject) {
var xhr = new XMLHttpRequest();
xhr.open(method, url);
xhr.onload = function () {
if (xhr.status == 200) {
resolve(xhr.responseText);
}
else {
reject(new Error(xhr.responseText));
}
};
xhr.send();
});
}

Simple async request:
function get(url, callback) {
var getRequest = new XMLHttpRequest();
getRequest.open("get", url, true);
getRequest.addEventListener("readystatechange", function() {
if (getRequest.readyState === 4 && getRequest.status === 200) {
callback(getRequest.responseText);
}
});
getRequest.send();
}

Ajax
You'd be best off using a library such as Prototype or jQuery.

// Create a request variable and assign a new XMLHttpRequest object to it.
var request = new XMLHttpRequest()
// Open a new connection, using the GET request on the URL endpoint
request.open('GET', 'restUrl', true)
request.onload = function () {
// Begin accessing JSON data here
}
// Send request
request.send()

In pure javascript and returning a Promise:
httpRequest = (url, method = 'GET') => {
return new Promise((resolve, reject) => {
const xhr = new XMLHttpRequest();
xhr.open(method, url);
xhr.onload = () => {
if (xhr.status === 200) { resolve(xhr.responseText); }
else { reject(new Error(xhr.responseText)); }
};
xhr.send();
});
}

If you want to use the code for a Dashboard widget, and you don't want to include a JavaScript library in every widget you created, then you can use the object XMLHttpRequest that Safari natively supports.
As reported by Andrew Hedges, a widget doesn't have access to a network, by default; you need to change that setting in the info.plist associated with the widget.

You can do it with pure JS too:
// Create the XHR object.
function createCORSRequest(method, url) {
var xhr = new XMLHttpRequest();
if ("withCredentials" in xhr) {
// XHR for Chrome/Firefox/Opera/Safari.
xhr.open(method, url, true);
} else if (typeof XDomainRequest != "undefined") {
// XDomainRequest for IE.
xhr = new XDomainRequest();
xhr.open(method, url);
} else {
// CORS not supported.
xhr = null;
}
return xhr;
}
// Make the actual CORS request.
function makeCorsRequest() {
// This is a sample server that supports CORS.
var url = 'http://html5rocks-cors.s3-website-us-east-1.amazonaws.com/index.html';
var xhr = createCORSRequest('GET', url);
if (!xhr) {
alert('CORS not supported');
return;
}
// Response handlers.
xhr.onload = function() {
var text = xhr.responseText;
alert('Response from CORS request to ' + url + ': ' + text);
};
xhr.onerror = function() {
alert('Woops, there was an error making the request.');
};
xhr.send();
}
See: for more details: html5rocks tutorial

Here is an alternative to xml files to load your files as an object and access properties as an object in a very fast way.
Attention, so that javascript can him and to interpret the content correctly it is necessary to save your files in the same format as your HTML page. If you use UTF 8 save your files in UTF8, etc.
XML works as a tree ok? instead of writing
<property> value <property>
write a simple file like this:
Property1: value
Property2: value
etc.
Save your file ..
Now call the function ....
var objectfile = {};
function getfilecontent(url){
var cli = new XMLHttpRequest();
cli.onload = function(){
if((this.status == 200 || this.status == 0) && this.responseText != null) {
var r = this.responseText;
var b=(r.indexOf('\n')?'\n':r.indexOf('\r')?'\r':'');
if(b.length){
if(b=='\n'){var j=r.toString().replace(/\r/gi,'');}else{var j=r.toString().replace(/\n/gi,'');}
r=j.split(b);
r=r.filter(function(val){if( val == '' || val == NaN || val == undefined || val == null ){return false;}return true;});
r = r.map(f => f.trim());
}
if(r.length > 0){
for(var i=0; i<r.length; i++){
var m = r[i].split(':');
if(m.length>1){
var mname = m[0];
var n = m.shift();
var ivalue = m.join(':');
objectfile[mname]=ivalue;
}
}
}
}
}
cli.open("GET", url);
cli.send();
}
now you can get your values efficiently.
getfilecontent('mesite.com/mefile.txt');
window.onload = function(){
if(objectfile !== null){
alert (objectfile.property1.value);
}
}
It's just a small gift to contibute to the group. Thanks of your like :)
If you want to test the function on your PC locally, restart your browser with the following command (supported by all browsers except safari):
yournavigator.exe '' --allow-file-access-from-files

<button type="button" onclick="loadXMLDoc()"> GET CONTENT</button>
<script>
function loadXMLDoc() {
var xmlhttp = new XMLHttpRequest();
var url = "<Enter URL>";``
xmlhttp.onload = function () {
if (xmlhttp.readyState == 4 && xmlhttp.status == "200") {
document.getElementById("demo").innerHTML = this.responseText;
}
}
xmlhttp.open("GET", url, true);
xmlhttp.send();
}
</script>

How to load a json file with javascript locally without Jquery?

I'm creating a website to progress in javascript and I have a little problem, every ways I try, my browser doesn't want to load my json file.
I tried many codes i found on internet but none of them work (or I don't know how to make them work). Finally i fond this one which is quite easy to understand but yhis one too doesn't work and always return an error message.
function loadJSON(path,success, error)
{
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function()
{
if (xhr.readyState === XMLHttpRequest.DONE) {
if (xhr.status === 1) {
if (success)
success(JSON.parse(xhr.responseText));
} else {
if (error)
error(xhr);
}
}
};
xhr.open("GET", path , true);
xhr.send();
}
function test()
{
loadJSON('test.json', function(data) { console.log(data); }, function(xhr) { console.error(xhr); });
}
I run the test function but everytimes, the console return me an error. Someone have an idea to solve my problem ?

status is the HTTP response code.
200 means the request has been successful. The status will most likely never be 1.
Here is a list of HTTP codes
As a solution, I suggest using the fetch API, which is the modern way to query files.
Here are some examples on how to use it
If you really want to use AJAX, use this :
var request = new XMLHttpRequest();
request.open('GET', '/my/url', true);
request.onload = function() {
if (this.status >= 200 && this.status < 400) {
// Success!
var resp = this.response;
} else {
// We reached our target server, but it returned an error
}
};
request.onerror = function() {
// There was a connection error of some sort
};
request.send();
Source : You Might Not Need jQuery

How to detect if a file exists in JavaScript accounting for 404 handler

In my website I am currently trying to write code to turn a link into a formatted attachment .
I am trying to write code to detect if the file exists
function doesFileExist(urlToFile) {
var xhr = new XMLHttpRequest();
xhr.open('HEAD', urlToFile, false);
if (xhr.status == "404") {
return false;
} else {
return true;
}
}
alert(doesFileExist("http://hexbugman213.net/favicon.png"));
However, I noticed a problem. When the website has a 404 handler like .htaccess, and I try to test it with the file, it sees that the website didn't return a 404, and therefore still says it exists.
function doesFileExist(urlToFile) {
var xhr = new XMLHttpRequest();
xhr.open('HEAD', urlToFile, false);
if (xhr.status == "404") {
return false;
} else {
return true;
}
}
alert(doesFileExist("http://hexbugman213.net/thisfiledoesntexist.mp3"));
Is there any way I can account for this and have it return "false" when the file doesn't exist even if there's a 404 handler?

You need to call the send() function on the XMLHttpRequest to make it actually make the request. See: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/send
Also, you may run into cross origin issues depending on exactly what URL you're trying to retrieve and where you're hosting the page from. Mozilla has some documentation on the subject if you're not familiar with it: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
Here is an improved version of your JavaScript that checks for exceptions and calls the send() function.
function doesFileExist(urlToFile) {
try {
var xhr = new XMLHttpRequest();
xhr.open('HEAD', urlToFile, false);
xhr.send();
alert(xhr.status)
if (xhr.status !== 200) {
return false;
} else {
return true;
}
} catch (e) {
alert(e);
return false;
}
}
alert(doesFileExist("https://server.test-cors.org/server?enable=true&status=200&credentials=false"));
alert(doesFileExist("https://server.test-cors.org/server?enable=true&status=404&credentials=false"));
alert(doesFileExist("https://www.google.com/"));
alert(doesFileExist("http://hexbugman213.net/thisfiledoesntexist.mp3"));
The host: https://www.test-cors.org/ in the example is useful for testing CORS.

Undefined returned from file existence check

I'm checking if a file at a certain local URL exists via a XMLHttpRequest, kind of a workaround peek at the filesystem. Using the pingFile function described below, I try to see if I get a 200 or 404 for a given file and perform some actions depending on that result.
function pingFile(theURL, callback)
{
var req = new XMLHttpRequest();
req.onreadystatechange = function() {
if (this.readyState === this.DONE) {
if (callback !== null) {
return callback(this.status);
} else {
return this.status;
}
}
};
req.open("HEAD", theURL);
req.send();
}
var q = pingFile('images/image1.png', null);
However, when I check the value of q, it is always undefined. I'm missing something about the asynchronous nature of an XHR here, I think, but I haven't been able to find where to wait so that this.status has either of the values I would expect from a file check.
EDIT: I've tried adding return 4; after req.send(); and that always gives q the value 4 regardless of whether the file is there.
How do I get the status value of a XMLHttpRequest back from the function it's in?

For async operations you could use callbacks or promises. Here is a simple example with callbacks:
(function () {
function pingFile(theURL, success, error) {
var req = new XMLHttpRequest();
req.onload = function (e) {
if (this.status === 200) {
success(e);
} else {
error(e);
}
};
req.open("HEAD", theURL);
req.send();
}
function fileExist(e) {
alert('File exist!');
}
function fileNotExist(e) {
alert('File does not exist!');
}
pingFile('images/image1.png', fileExist, fileNotExist);
}());

CORS request firing without sending form data on window.onbeforeunload event in IE9

I've got a pretty simple function which is designed to grab the form data and send it via a CORS request. Basically it looks like this...
window.onbeforeunload = function() {
formData = getFormData();
logAbandonment(formData);
// return formData;
// alert(formData);
}
function logAbandonment(formData)
{
if(!cors_request) {
cors_request = true;
} else {
return;
}
var url = 'http://mydomain.lan/sub/index.php';
var xhr = createCORSRequest('POST', url);
if (!xhr) {
console.log('Error: CORS not supported.');
}
xhr.send(formData);
}
function createCORSRequest(method, url)
{
var xhr = new XMLHttpRequest();
if ("withCredentials" in xhr) {
// Check if the XMLHttpRequest object has a "withCredentials" property.
// "withCredentials" only exists on XMLHTTPRequest2 objects.
xhr.open(method, url, true);
} else if (typeof XDomainRequest != "undefined") {
// Otherwise, check if XDomainRequest.
// XDomainRequest only exists in IE, and is IE's way of making CORS requests.
xhr = new XDomainRequest();
xhr.open(method, url);
xhr.onprogress = function () { };
xhr.ontimeout = function () { };
xhr.onerror = function () { };
xhr.onload = function() { };
} else {
// Otherwise, CORS is not supported by the browser.
xhr = null;
}
return xhr;
}
function getFormData()
{
if(typeof FormData == 'undefined') {
return serialize(document.getElementById('AppForm'));
} else {
return new FormData(document.getElementById('AppForm'));
}
}
Because this is IE9 I am working with, I am using the XDomainRequest javascript object.
It is successfully firing the ajax request, but here is where I am having a problem. It is firing it without sending the formData unless I uncomment either of the return or alert lines, in which case it works perfectly. When I do that, I can see the correct data it is supposed to be saying in the alert.
Another thing I noticed is this only happens when I either close the browser or close the tab. If I refresh the page, it works exactly like I want it to.
I thought maybe IE9 had some weird method of destroying the dom before the request was finished going out, but unfortunately, I can't figure out a way to set this to async false on XDomainRequest.
I've also tried setting a timeout, but that seems to break it completely.

Not an answer as much as a work-around, but I found this works perfectly when appending the query string onto the end of the url when calling xdr's open method.