For the past days, we've been trying to develop a Devtools extension that could intercept only XHR requests. We can use the chrome.webRequest API on a normal extension, but that is not possible on a Devtools Extension Panel. We tried to used the devtools.network, but it catches all requests.
Is there a way to catch only the XHR requests?
Thanks in advance.
You can use the chrome.devtools.network API to get the HAR, and then you can determine whether a request is XHR or not, filtering the output.
I'm not totally sure how DevTools determines this, but the X-Requested-With header is (typically) sent when AJAX requests are made. It is a non-standard, but is used widely. You can check for the XMLHttpRequest value in the HAR.
It's possible this doesn't catch all the requests, and there might be some other data DevTools uses, but here's a little snippet I created that will filter the HAR based on this header.
chrome.devtools.network.getHAR(function(result) {
var entries = result.entries;
var xhrEntries = entries.filter(function(entry) {
var headers = entry.request.headers;
var xhrHeader = headers.filter(function(header) {
return header.name.toLowerCase() === 'x-requested-with'
&& header.value === 'XMLHttpRequest';
});
return xhrHeader.length > 0;
});
console.log(xhrEntries);
});
Note. You can access the HAR data in the same way, per request, as it finishes, using the chrome.devtools.network.onRequestFinished event.
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've been looking for an AJAX function that receives an URL and then returns the JSON object.
Let's say I need to display some Users info from a JSON in URL1 and also mix that display with some Posts info from a JSON in URL2.
I'll like to do this without JQquery.
Let's say something like this:
function loadJSON(path, success, error)
{
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function()
{
if (xhr.readyState === XMLHttpRequest.DONE) {
if (xhr.status === 200) {
if (success)
success(JSON.parse(xhr.responseText));
} else {
if (error)
error(xhr);
}
}
};
xhr.open("GET", path, true);
xhr.send();
}
function getInfo(){
var users, posts;
loadJSON('http://.com/users',
function(dataU) {
users = dataU;
},
function(xhr) { console.error(xhr); }
);
loadJSON('http://.com/posts',
function(dataP) {
posts = dataP;
},
function(xhr) { console.error(xhr); }
);
console.log(users);
console.log(posts);
}
getInfo();
To achieve this without jQuery, you can fall back to plain JavaScript XMLHttpRequests. This will allow you to establish an HTTP connection with a remote host and e.g. GET data.
To get started with those requests, you can have a look at MDN's getting started guide.
The JSON.parse() function will help you convert the JSON string into a JavaScript object.
As an alternative to XMLHttpRequests, you can also look into the fetch API. It provides a cleaner interface for HTTP calls. Since it is still experimental however, you may want to use a polyfill.
With or without jQuery the XMLHttpRequest objest is asynchronous. jQuery uses it internally. FIY AJAX stands for Asynchronous Javascript And Xml. It means that you cannot receive a synchronous result from an asynchronous function. But you can and should use the result in a callback function you send to the request.
So correct usage is to call console.log (or whatever you want) from success or error callbacks.
There are known solution how to degrade gracefully when XMLHttpRequest is not available. Among these solutions are create and append script or iframe and then read from their .onload handlers. All of them are asynchronous and all previous considerations apply directly to them.
You Cannot Receive Synchronous Result From Asynchronous Function.
I hold this truth against all downvotes.
In the process of working on a simple project (or at least I thought to be simple) Where a user clicks a button, and a random saying generated from php appears in the above textbox. I do not have access to the php file so I can't see the code and feel a bit lost. The problem I'm having I believe, is an error in the way Im handling the response from the server (the handleServerResponse function). Any advice would be appreciated.
In an attempt to debug, I've seen this message: (I've changed the url)
XMLHttpRequest cannot load http:somephp.php. No
'Access-Control-Allow-Origin' header is present on the requested
resource. Origin 'null' is therefore not allowed access.
the code thus far:
var xmlHttp = createXmlHttpRequestObject();
function createXmlHttpRequestObject(){
var xmlHttp;
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 1");
else
return xmlHttp;
}
$("#BtnReset").click(function () {
$("#TBSaying").val("");
})
$("#BtnGetSaying").click(function () {
process();
})
function process(){
if(xmlHttp.readyState==0 || xmlHttp.readyState==4){
xmlHttp.open("GET", "http://somephp.php", true);
xmlHttp.onreadystatechange = handleServerResponse;
xmlHttp.send(null);
}else{
setTimeout('process()', 1000);
}
}
function handleServerResponse(){
if(xmlHttp.readyState==4){
if(xmlHttp.status==200){
xmlResponse = xmlHttp.responseXML;
xmlDocumentElement = xmlResponse.documentElement;
message = xmlDocumentElement.firstChild.data
$("#TBSaying").val(message);
}else{
alert('error 2');
}
}
}
Read through the JQuery documentation and started fresh, uploaded it to the same server in which the php resides and it works. here is the final code: Thanks to all that advised!
$("#BtnReset").click(function () {
$("#TBSaying").val("");
})
$("#BtnGetSaying").click(function () {
process();
})
function process(){
// AJAX Code To Submit Form.
$.get("http://somephp.php",function(data){
$("#TBSaying").val(data);
});
}
Ajax calls from a browser are restricted by what is called "same origin restrictions". Basically this means that, by default, you can only make an Ajax call back to the same server that the web page came from. That means you cannot make a regular Ajax call to a server on another domain, port or protocol.
You can read about the same origin policy here.
There are a three ways around this restriction, but all require cooperation from a server.
CORS. The server you are making the request from puts headers in its responses that tell the browser whether a cross origin request is allowed or even what domains it is allowed from. This gives the browser permission to complete Ajax calls that are not from the same origin.
JSONP. You can read more about JSONP here. Basically, you request a script from the target server and the script is coded in such a way that it will provide you the answer you want (usually in the JSON data format).
Server proxy. You find or code a server proxy that will request the data from the other server for you. Because server to server communication is not limited by the same origin restrictions, you can sometimes find another server that allows cross-origin requests to it that will then get the data for you and then return it to you.
Your javascript seems horrible, but alas, wrong
"Access-Control-Allow-Origin" is a server-sided (php?) bug, sorry.
tell the server guys to add something like
header("Access-Control-Allow-Origin: *");
to see if your javascript is correct ^^
on a sidenote,
alert("Error 1"); should probably use console.log or throw new Error() instead..
why have xmlHttp as a global, can just use process(e){ var xhr=e.target;...} instead
don't do this setTimeout('process()', 1000); , do setTimeout(process, 1000);
Is it possible to prevent the browser from following redirects when sending XMLHttpRequest-s (i.e. to get the redirect status code back and handle it myself)?
Not according to the W3C standard for the XMLHttpRequest object (emphasis added):
If the response is an HTTP redirect:
If the origin of the URL conveyed by the Location header is same origin
with the XMLHttpRequest origin and the
redirect does not violate infinite
loop precautions, transparently
follow the redirect while observing
the same-origin request event rules.
They were considering it for a future release:
This specification does not include
the following features which are being
considered for a future version of
this specification:
Property to disable following redirects;
but the latest specification no longer mentions this.
The new Fetch API supports different modes of redirect handling: follow, error, and manual, but I can't find a way to view the new URL or the status code when the redirection has been canceled. You just can stop the redirection itself, and then it looks like an error (empty response). If that's all you need, you are good to go. Also you should be aware that the requests made via this API are not cancelable yet. They are now.
As for XMLHttpRequest, you can HEAD the server and inspect whether the URL has changed:
var http = new XMLHttpRequest();
http.open('HEAD', '/the/url');
http.onreadystatechange = function() {
if (this.readyState === this.DONE) {
console.log(this.responseURL);
}
};
http.send();
You won't get the status code, but will find the new URL without downloading the whole page from it.
No you there isn't any place in the API exposed by XMLHttpRequest that allows you to override its default behaviour of following a 301 or 302 automatically.
If the client is running IE on windows then you can use WinHTTP instead to set an option to prevent that behaviour but thats a very limiting solution.
You can use responseURL property to get the redirect destination or check whether the response was ultimately fetched from a location you accept.
This of course means the result is fetched anyway, but at least you can get the necessary info about the redirect destination and for example detect conditions when you would like to discard the response.
I extended user's answer to include an abort() call. It seems like this prevents the server from sending too much data when all you want is the redirect url.
var url = 'the url'
var http = new XMLHttpRequest();
http.open('GET', url);
http.onreadystatechange = function() {
if (this.readyState === this.DONE) {
console.log(this.responseURL)
this.abort() // This seems to stop the response
}
}
http.send()
In real life I wrapped the above code in a promise, but it made the code hard to read.
Also, I don't understand why getting the redirect url needs to be this difficult, but that is a question for another time and place.
It is not possible to handle redirect or 302 status at client side as answered in other comments. However you can prevent redirection. To do that you can set request header "X-Requested-With" with "XMLHttpRequest"
xhttp.setRequestHeader("X-Requested-With", "XMLHttpRequest");
This should be done after open but before send. Example below
let xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function () {
if (this.readyState == 4 && this.status == 200) {
reqObj.success(JSON.parse(this.responseText))
} else if (this.status != 200) {
reqObj.error(this.statusText)
}
};
xhttp.open(reqObj.type, reqObj.url, reqObj.async);
xhttp.setRequestHeader("X-Requested-With", "XMLHttpRequest");
xhttp.send();