How do I access a page's HTTP response headers via JavaScript?
Related to this question, which was modified to ask about accessing two specific HTTP headers.
Related:
How do I access the HTTP request header fields via JavaScript?
It's not possible to read the current headers. You could make another request to the same URL and read its headers, but there is no guarantee that the headers are exactly equal to the current.
Use the following JavaScript code to get all the HTTP headers by performing a get request:
var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
alert(headers);
Unfortunately, there isn't an API to give you the HTTP response headers for your initial page request. That was the original question posted here. It has been repeatedly asked, too, because some people would like to get the actual response headers of the original page request without issuing another one.
For AJAX Requests:
If an HTTP request is made over AJAX, it is possible to get the response headers with the getAllResponseHeaders() method. It's part of the XMLHttpRequest API. To see how this can be applied, check out the fetchSimilarHeaders() function below. Note that this is a work-around to the problem that won't be reliable for some applications.
myXMLHttpRequest.getAllResponseHeaders();
The API was specified in the following candidate recommendation for XMLHttpRequest: XMLHttpRequest - W3C Candidate Recommendation 3 August 2010
Specifically, the getAllResponseHeaders() method was specified in the following section: w3.org: XMLHttpRequest: the getallresponseheaders() method
The MDN documentation is good, too: developer.mozilla.org: XMLHttpRequest.
This will not give you information about the original page request's HTTP response headers, but it could be used to make educated guesses about what those headers were. More on that is described next.
Getting header values from the Initial Page Request:
This question was first asked several years ago, asking specifically about how to get at the original HTTP response headers for the current page (i.e. the same page inside of which the javascript was running). This is quite a different question than simply getting the response headers for any HTTP request. For the initial page request, the headers aren't readily available to javascript. Whether the header values you need will be reliably and sufficiently consistent if you request the same page again via AJAX will depend on your particular application.
The following are a few suggestions for getting around that problem.
1. Requests on Resources which are largely static
If the response is largely static and the headers are not expected to change much between requests, you could make an AJAX request for the same page you're currently on and assume that they're they are the same values which were part of the page's HTTP response. This could allow you to access the headers you need using the nice XMLHttpRequest API described above.
function fetchSimilarHeaders (callback) {
var request = new XMLHttpRequest();
request.onreadystatechange = function () {
if (request.readyState === XMLHttpRequest.DONE) {
//
// The following headers may often be similar
// to those of the original page request...
//
if (callback && typeof callback === 'function') {
callback(request.getAllResponseHeaders());
}
}
};
//
// Re-request the same page (document.location)
// We hope to get the same or similar response headers to those which
// came with the current page, but we have no guarantee.
// Since we are only after the headers, a HEAD request may be sufficient.
//
request.open('HEAD', document.location, true);
request.send(null);
}
This approach will be problematic if you truly have to rely on the values being consistent between requests, since you can't fully guarantee that they are the same. It's going to depend on your specific application and whether you know that the value you need is something that won't be changing from one request to the next.
2. Make Inferences
There are some BOM properties (Browser Object Model) which the browser determines by looking at the headers. Some of these properties reflect HTTP headers directly (e.g. navigator.userAgent is set to the value of the HTTP User-Agent header field). By sniffing around the available properties you might be able to find what you need, or some clues to indicate what the HTTP response contained.
3. Stash them
If you control the server side, you can access any header you like as you construct the full response. Values could be passed to the client with the page, stashed in some markup or perhaps in an inlined JSON structure. If you wanted to have every HTTP request header available to your javascript, you could iterate through them on the server and send them back as hidden values in the markup. It's probably not ideal to send header values this way, but you could certainly do it for the specific value you need. This solution is arguably inefficient, too, but it would do the job if you needed it.
Using XmlHttpRequest you can pull up the current page and then examine the http headers of the response.
Best case is to just do a HEAD request and then examine the headers.
For some examples of doing this have a look at http://www.jibbering.com/2002/4/httprequest.html
Just my 2 cents.
A solution with Service Workers
Service workers are able to access network information, which includes headers. The good part is that it works on any kind of request, not just XMLHttpRequest.
How it works:
Add a service worker on your website.
Watch every request that's being sent.
Make the service worker fetch the request with the respondWith function.
When the response arrives, read the headers.
Send the headers from the service worker to the page with the postMessage function.
Working example:
Service workers are a bit complicated to understand, so I've built a small library that does all this. It is available on github: https://github.com/gmetais/sw-get-headers.
Limitations:
the website needs to be on HTTPS
the browser needs to support the Service Workers API
the same-domain/cross-domain policies are in action, just like on XMLHttpRequest
Another way to send header information to JavaScript would be through cookies. The server can extract whatever data it needs from the request headers and send them back inside a Set-Cookie response header — and cookies can be read in JavaScript. As keparo says, though, it's best to do this for just one or two headers, rather than for all of them.
(2021) An answer without additional HTTP call
While it's not possible in general to read arbitrary HTTP response headers of the top-level HTML navigation, if you control the server (or middleboxes on the way) and want to expose some info to JavaScript that can't be exposed easily in any other way than via a header:
You may use Server-Timing header to expose arbitrary key-value data, and it will be readable by JavaScript.
(*in supported browsers: Firefox 61, Chrome 65, Edge 79; no Safari yet and no immediate plans for shipping as of 2021.09; no IE)
Example:
server-timing: key;desc="value"
You can use this header multiple times for multiple pieces of data:
server-timing: key1;desc="value1"
server-timing: key2;desc="value2"
or use its compact version where you expose multiple pieces of data in one header, comma-separated.
server-timing: key1;desc="value1", key2;desc="value2"
Example of how Wikipedia uses this header to expose info about cache hit/miss:
Code example (need to account for lack of browser support in Safari and IE):
if (window.performance && performance.getEntriesByType) { // avoid error in Safari 10, IE9- and other old browsers
let navTiming = performance.getEntriesByType('navigation')
if (navTiming.length > 0) { // still not supported as of Safari 14...
let serverTiming = navTiming[0].serverTiming
if (serverTiming && serverTiming.length > 0) {
for (let i=0; i<serverTiming.length; i++) {
console.log(`${serverTiming[i].name} = ${serverTiming[i].description}`)
}
}
}
}
This logs cache = hit-front in supported browsers.
Notes:
as mentioned on MDN, the API is only supported over HTTPS
if your JS is served from another domain, you have to add Timing-Allow-Origin response header to make the data readable to JS (Timing-Allow-Origin: * or Timing-Allow-Origin: https://www.example.com)
Server-Timing headers support also dur(header) field, readable as duration on JS side, but it's optional and defaults to 0 in JS if not passed
regarding Safari support: see bug 1 and bug 2 and bug 3
You can read more on server-timing in this blog post
Note that performance entries buffers might get cleaned by JS on the page (via an API call), or by the browser, if the page issues too many calls for subresources. For that reason, you should capture the data as soon as possible, and/or use PerformanceObserver API instead. See the blog post for details.
For those looking for a way to parse all HTTP headers into an object that can be accessed as a dictionary headers["content-type"], I've created a function parseHttpHeaders:
function parseHttpHeaders(httpHeaders) {
return httpHeaders.split("\n")
.map(x=>x.split(/: */,2))
.filter(x=>x[0])
.reduce((ac, x)=>{ac[x[0]] = x[1];return ac;}, {});
}
var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = parseHttpHeaders(req.getAllResponseHeaders());
// Now we can do: headers["content-type"]
You can't access the http headers, but some of the information provided in them is available in the DOM. For example, if you want to see the http referer (sic), use document.referrer. There may be others like this for other http headers. Try googling the specific thing you want, like "http referer javascript".
I know this should be obvious, but I kept searching for stuff like "http headers javascript" when all I really wanted was the referer, and didn't get any useful results. I don't know how I didn't realize I could make a more specific query.
Like many people I've been digging the net with no real answer :(
I've nevertheless find out a bypass that could help others. In my case I fully control my web server. In fact it is part of my application (see end reference). It is easy for me to add a script to my http response. I modified my httpd server to inject a small script within every html pages. I only push a extra 'js script' line right after my header construction, that set an existing variable from my document within my browser [I choose location], but any other option is possible. While my server is written in nodejs, I've no doubt that the same technique can be use from PHP or others.
case ".html":
response.setHeader("Content-Type", "text/html");
response.write ("<script>location['GPSD_HTTP_AJAX']=true</script>")
// process the real contend of my page
Now every html pages loaded from my server, have this script executed by the browser at reception. I can then easily check from JavaScript if the variable exist or not. In my usecase I need to know if I should use JSON or JSON-P profile to avoid CORS issue, but the same technique can be used for other purposes [ie: choose in between development/production server, get from server a REST/API key, etc ....]
On the browser you just need to check variable directly from JavaScript as in my example, where I use it to select my Json/JQuery profile
// Select direct Ajax/Json profile if using GpsdTracking/HttpAjax server otherwise use JsonP
var corsbypass = true;
if (location['GPSD_HTTP_AJAX']) corsbypass = false;
if (corsbypass) { // Json & html served from two different web servers
var gpsdApi = "http://localhost:4080/geojson.rest?jsoncallback=?";
} else { // Json & html served from same web server [no ?jsoncallback=]
var gpsdApi = "geojson.rest?";
}
var gpsdRqt =
{key :123456789 // user authentication key
,cmd :'list' // rest command
,group :'all' // group to retreive
,round : true // ask server to round numbers
};
$.getJSON(gpsdApi,gpsdRqt, DevListCB);
For who ever would like to check my code:
https://www.npmjs.org/package/gpsdtracking
Allain Lalonde's link made my day.
Just adding some simple working html code here.
Works with any reasonable browser since ages plus IE9+ and Presto-Opera 12.
<!DOCTYPE html>
<title>(XHR) Show all response headers</title>
<h1>All Response Headers with XHR</h1>
<script>
var X= new XMLHttpRequest();
X.open("HEAD", location);
X.send();
X.onload= function() {
document.body.appendChild(document.createElement("pre")).textContent= X.getAllResponseHeaders();
}
</script>
Note: You get headers of a second request, the result may differ from the initial request.
Another way is the more modern fetch() API
https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
Per caniuse.com it's supported by Firefox 40, Chrome 42, Edge 14, Safari 11
Working example code:
<!DOCTYPE html>
<title>fetch() all Response Headers</title>
<h1>All Response Headers with fetch()</h1>
<script>
var x= "";
if(window.fetch)
fetch(location, {method:'HEAD'})
.then(function(r) {
r.headers.forEach(
function(Value, Header) { x= x + Header + "\n" + Value + "\n\n"; }
);
})
.then(function() {
document.body.appendChild(document.createElement("pre")).textContent= x;
});
else
document.write("This does not work in your browser - no support for fetch API");
</script>
If we're talking about Request headers, you can create your own headers when doing XmlHttpRequests.
var request = new XMLHttpRequest();
request.setRequestHeader("X-Requested-With", "XMLHttpRequest");
request.open("GET", path, true);
request.send(null);
To get the headers as an object which is handier (improvement of Raja's answer):
var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
headers = headers.split(/\n|\r|\r\n/g).reduce(function(a, b) {
if (b.length) {
var [ key, value ] = b.split(': ');
a[key] = value;
}
return a;
}, {});
I've just tested, and this works for me using Chrome Version 28.0.1500.95.
I was needing to download a file and read the file name. The file name is in the header so I did the following:
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.responseType = "blob";
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
success(xhr.response); // the function to proccess the response
console.log("++++++ reading headers ++++++++");
var headers = xhr.getAllResponseHeaders();
console.log(headers);
console.log("++++++ reading headers end ++++++++");
}
};
Output:
Date: Fri, 16 Aug 2013 16:21:33 GMT
Content-Disposition: attachment;filename=testFileName.doc
Content-Length: 20
Server: Apache-Coyote/1.1
Content-Type: application/octet-stream
This is my script to get all the response headers:
var url = "< URL >";
var req = new XMLHttpRequest();
req.open('HEAD', url, false);
req.send(null);
var headers = req.getAllResponseHeaders();
//Show alert with response headers.
alert(headers);
Having as a result the response headers.
This is a comparison test using Hurl.it:
Using mootools, you can use this.xhr.getAllResponseHeaders()
This is an old question. Not sure when support became more broad, but getAllResponseHeaders() and getResponseHeader() appear to now be fairly standard: http://www.w3schools.com/xml/dom_http.asp
As has already been mentioned, if you control the server side then it should be possible to send the initial request headers back to the client in the initial response.
In Express, for example, the following works:
app.get('/somepage', (req, res) => {
res.render('somepage.hbs', {headers: req.headers});
})
The headers are then available within the template, so could be hidden visually but included in the markup and read by clientside javascript.
I think the question went in the wrong way,
If you want to take the Request header from JQuery/JavaScript the answer is simply No. The other solutions is create a aspx page or jsp page then we can easily access the request header.
Take all the request in aspx page and put into a session/cookies then you can access the cookies in JavaScript page..
I have the following code to check whether the webpage can be framed or not at all:
var req = new XMLHttpRequest();
var test = req.open('GET', link, false);
console.log("test",test); //ALWAYS undefined
if(req.send(null)){ //ALWAYS throws error NS_ERROR_FAILURE
var headers = req.getAllResponseHeaders().toLowerCase();
console.log("headers");
}else{
console.log("FAILED");
}
I tested it with several links, frameable or not, but always fails. Do you know exactly why?
Links:
http://www.joomlaworks.net/images/demos/galleries/abstract/7.jpg
http://www.facebook.com (...)
test is undefined because open() is declared void, it does not return any value. Check out MDN on the open method.
Why are you passing null to send? (see edit) If you intend to call the overload of send that doesn't take any argument you should just call req.send(); instead if you want to call another version of the method you should pass a Blob, Document, DOMString or FormData, but null won't work.
EDIT: Often the method is invoked as send(null); it seems to be because at some point in history (is that old?) the argument of send was mandatory. This question unravels the mystery.
Moreover, again send doesn't return any value so the condition in the if will never evaluate true. MDN documents also the send method.
Last, you are performing a cross-domain request, i.e. you're asking for content that is located on another domain. XMLHttpRequest doesn't handle that, most likely you will end up with this error:
XMLHttpRequest cannot load link. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin origin is therefore not allowed access.
Check out this question and this on StackOverflow if you need more information about that.
You may want to take a look at Using XMLHttpRequest again on the MDN network, it has many reliable examples that can help you get acquainted with these requests.
EDIT: expanding on the topic iframe embeddability.
Detecting reliably if a website can be embedded in an iframe is difficult, as this question shows. Detecting (or preventing) frame buster in JavaScript is like a dog chasing its own tail.
Nevertheless, a website that doesn't want to be incorporated, hopefully would send the X-Frame-Options: DENY header in its response. This is not very useful, because you can't perform cross domain requests: your request would fail before getting to know if the X-Frame-Options header is even set. For completeness, this is the way of checking if the response to an XMLHttpRequest contains a given header (but note that this would work only within the same domain, which is presumably under your control, and you would know already if a page is 'frameable'):
function checkXFrame() {
var xframe = this.getResponseHeader("X-Frame-Options");
if (!xframe) {
alert("Frameable.");
return;
}
xframe = xframe.toLowerCase();
if (xframe == "deny") {
alert("Not frameable.");
} else if (xframe == "sameorigin") {
alert("Frameable within the same domain.");
} else if (xframe.startsWith("allow-from")) {
alert("Frameable from certain domains.");
} else {
alert("Someone sent a weird header.");
}
}
var oReq = new XMLHttpRequest();
oReq.open("HEAD" /* use HEAD if you only need the headers! */, "yourpage.html");
oReq.onload = checkXFrame;
oReq.send();
(this code doesn't check for 404 or any other error!)
I was looking into the concept of JSONP callback function. I read some articles regarding that and wanted to get a good grasp of the concept of JSONP.
So, I uploaded one json file to the server - json file
And here is the js code which I wrote to retrieve the data. The call is made from localhost to the abhishekprakash.com.
var xhr;
var dataList;
xhr = new XMLHttpRequest();
xhr.open('GET', 'http://abhishekprakash.com/script/example.json?callback=func_callbk', true);
xhr.send();
func_callback = function(data){
alert(data.data.people[0].id);
}
xhr.onreadystatechange = function(){
if(xhr.readyState == 4){
console.log(dataList);
}
};
And this is the response that I get in the console:
The callback function is called but it does not contain the Json data.
What am I missing?
Any help is appreciated.
Thanks
That example service returns JSON, not JSONP.
The point of JSONP is that due to Same Origin Policy security restrictions, Javascript from domain A cannot make a GET request to resources on domain B; in other words a script cannot retrieve data cross-domain.
JSONP solves this by making domain B explicitly cooperate in the cross-domain data sharing. The script from domain A specifies the name of a callback function and embeds the URL of domain B in the document as if it were including a regular external Javascript file. Domain B then outputs data like this:
callbackFuncName({ data : foo, ... });
That means domain B explicitly outputs a Javascript snippet which calls the specified callback function with the data.
So, unless domain B explicitly cooperates in this, you cannot simply get a JSONP response from it.
The XHR is constrained by cross-domain rules; to use JSONP you need to add a script element:
function func_callbk()
{
console.log(arguments);
}
var s = document.createElement('script');
s.type = 'text/javascript';
s.src = 'http://abhishekprakash.com/script/example.json?callback=func_callbk';
var h = document.getElementsByTagName('script')[0];
h.parentNode.insertBefore(s, h);
As pointed out by Ian in the comments, the proper response of your server should be something like this:
func_callbk('hello world')
Update
If you wish to make this work without JSONP (e.g. if the response should always be JSON), you need to look into CORS as explained in this answer.
Using getAllResponseHeaders in the xhr object, is possible to get all the response headers after an ajax call.
But I can't found a way to get the Request headers string, is that possible ?
If this is for debugging purposes then you can just use Firebug or Chrome Developer Tools (and whatever the feature is called in IE) to examine the network traffic from your browser to the server.
An alternative would be to use something like this script:
$.ajax({
url: 'someurl',
headers:{'foo':'bar'},
complete: function() {
alert(this.headers.foo);
}
});
However I think only the headers already defined in headers is available (not sure what happens if the headers are altered (for instance in beforeSend).
You could read a bit more about jQuery ajax at: http://api.jquery.com/jQuery.ajax/
EDIT: If you want to just catch the headers on all calls to setRequestHeader on the XMLHttpRequest then you can just wrapp that method. It's a bit of a hack and of course you would need to ensure that the functions wrapping code below is run before any of the requests take place.
// Reasign the existing setRequestHeader function to
// something else on the XMLHtttpRequest class
XMLHttpRequest.prototype.wrappedSetRequestHeader =
XMLHttpRequest.prototype.setRequestHeader;
// Override the existing setRequestHeader function so that it stores the headers
XMLHttpRequest.prototype.setRequestHeader = function(header, value) {
// Call the wrappedSetRequestHeader function first
// so we get exceptions if we are in an erronous state etc.
this.wrappedSetRequestHeader(header, value);
// Create a headers map if it does not exist
if(!this.headers) {
this.headers = {};
}
// Create a list for the header that if it does not exist
if(!this.headers[header]) {
this.headers[header] = [];
}
// Add the value to the header
this.headers[header].push(value);
}
Now, once the headers have been set on an XMLHttpRequest instance we can get them out by examining xhr.headers e.g.
var xhr = new XMLHttpRequest();
xhr.open('get', 'demo.cgi');
xhr.setRequestHeader('foo','bar');
alert(xhr.headers['foo'][0]); // gives an alert with 'bar'
Something you could to is use Sinon's FakeXMLHttpRequest to replace your browser's XHR. It's described in this document on how to use it for testing but I'm pretty sure you can use the module for your debugging purposes.
What you need to do is:
var requests;
this.xhr = sinon.useFakeXMLHttpRequest();
this.xhr.onCreate = function(xhr) {
requests.push(xhr);
}
And then later on, you can check your requests array for headers by:
console.log(requests[0].requestHeaders);
To access your request headers.
So I have a bit of a problem. When I ask MooTools to send a request it comes back as failed every time. I can't seem to diagnose the problem either because if I try to get the returned header info the console just gives me "Refused to get unsafe header 'Status'" Message. The only thing I can think of is that the server isn't letting me access outside resources but maybe I just coded it wrong.
Here's the request code:
var finfo = current.textFontData();
var url = 'http://antiradiant.com/clients/TMW/rbwizard/mailer.php?s='+current.size+'&b='+current.box+'&l='+current.lidWood+'&c='+current.cartID+'&f='+finfo.font+'&l1='+finfo.line1+'&l2='+finfo.line2;
console.log(url);
var req = new Request({
url: url,
onSuccess: function() {
console.log('success');
//atc2.send();
},
onFailure: function() {
console.log('failure');
console.log(this.getHeader('Status'));
//atc2.send();
},
onException: function(headerName, value) {
console.log('exception');
console.log(headerName+': '+value);
}
});
req.send();
This code is derived from the resource rb_wizard.js (lines 81-103) on http://tylermorriswoodworking.myshopify.com/pages/recipe-box-wizard?b=maple&l=cherry&s=3x5&c=42042892
Mootools has a class called Request.JSONP that will help with your cross domain problem. Its sub class of the Request class, so your methods should work the same. I believe you need to call .post() or .get() at the end instead of send, but thats about all that should chnge. I'm not sure what version you're running on but here is the link tot he docs Mootools Request.JSONP
The error message "Refused to get unsafe header 'Status'" is spat out by WebKit based browsers (Safari, Chrome, etc) when you violate the cross-domain security model.
Therefore, it seems likely that the code you pasted is located on a domain other than antiradiant.com, and therefore is not allowed (by the browser) to request sites on antiradiant.com.
What I ended up doing was just using an iframe. All I really had to do was send data to another site and not receive any so it worked out.