In this guide, we'll take a look at how to use XMLHttpRequest to issue HTTP requests in order to exchange data between the web site and a server. Examples of both common and more obscure use cases for XMLHttpRequest are included.

To send an HTTP request, create an XMLHttpRequest object, open a URL, and send the request. After the transaction completes, the object will contain useful information such as the response body and the HTTP status of the result.

function reqListener () { console.log(this.responseText); } var oReq = new XMLHttpRequest(); oReq.addEventListener("load", reqListener); oReq.open("GET", "http://www.example.org/example.txt"); oReq.send();

Types of requests

A request made via XMLHttpRequest can fetch the data in one of two ways, asynchronously or synchronously. The type of request is dictated by the optional async argument (the third argument) that is set on the XMLHttpRequest.open() method. If this argument is true or not specified, the XMLHttpRequest is processed asynchronously, otherwise the process is handled synchronously. A detailed discussion and demonstrations of these two types of requests can be found on the synchronous and asynchronous requests page. Do not use synchronous requests outside Web Workers.

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.

Note: The constructor function XMLHttpRequest isn't limited to only XML documents. It starts with "XML" because when it was created the main format that was originally used for Asynchronous Data Exchange were XML

Handling responses

There are several types of response attributes defined by the living standard specification for the XMLHttpRequest() constructor. These tell the client making the XMLHttpRequest important information about the status of the response. Some cases where dealing with non-text response types may involve some manipulation and analysis are outlined in the following sections.

Analyzing and manipulating the responseXML property

If you use XMLHttpRequest to get the content of a remote XML document, the responseXML property will be a DOM object containing a parsed XML document. This could prove difficult to manipulate and analyze. There are four primary ways of analyzing this XML document:

Using XPath to address (or point to) parts of it. Manually Parsing and serializing XML to strings or objects. Using XMLSerializer to serialize DOM trees to strings or to files. RegExp can be used if you always know the content of the XML document beforehand. You might want to remove line breaks, if you use RegExp to scan with regard to line breaks. However, this method is a "last resort" since if the XML code changes slightly, the method will likely fail.

Note: XMLHttpRequest can now interpret HTML for you using the responseXML property. Read the article about HTML in XMLHttpRequest to learn how to do this.

Processing a responseText property containing an HTML document

If you use XMLHttpRequest to get the content of a remote HTML webpage, the responseText property is a string containing the raw HTML. This could prove difficult to manipulate and analyze. There are three primary ways to analyze and parse this raw HTML string:

Use the XMLHttpRequest.responseXML property as covered in the article HTML in XMLHttpRequest. Inject the content into the body of a document fragment via fragment.body.innerHTML and traverse the DOM of the fragment. RegExp can be used if you always know the content of the HTML responseText beforehand. You might want to remove line breaks, if you use RegExp to scan with regard to linebreaks. However, this method is a "last resort" since if the HTML code changes slightly, the method will likely fail.

Handling binary data

Although XMLHttpRequest is most commonly used to send and receive textual data, it can be used to send and receive binary content. There are several well tested methods for coercing the response of an XMLHttpRequest into sending binary data. These involve utilizing the overrideMimeType() method on the XMLHttpRequest object and is a workable solution.

var oReq = new XMLHttpRequest(); oReq.open("GET", url); // retrieve data unprocessed as a binary string oReq.overrideMimeType("text/plain; charset=x-user-defined"); /* ... */

However, more modern techniques are available, since the responseType attribute now supports a number of additional content types, which makes sending and receiving binary data much easier.

For example, consider this snippet, which uses the responseType of " arraybuffer " to fetch the remote content into a ArrayBuffer object, which stores the raw binary data.

var oReq = new XMLHttpRequest(); oReq.onload = function(e) { var arraybuffer = oReq.response; // not responseText /* ... */ } oReq.open("GET", url); oReq.responseType = "arraybuffer"; oReq.send();

For more examples check out the Sending and Receiving Binary Data page

Monitoring progress

XMLHttpRequest provides the ability to listen to various events that can occur while the request is being processed. This includes periodic progress notifications, error notifications, and so forth.

Support for DOM progress event monitoring of XMLHttpRequest transfers follows the specification for progress events: these events implement the ProgressEvent interface. The actual events you can monitor to determine the state of an ongoing transfer are:

progress The amount of data that has been retrieved has changed. load The transfer is complete; all data is now in the response

var oReq = new XMLHttpRequest(); oReq.addEventListener("progress", updateProgress); oReq.addEventListener("load", transferComplete); oReq.addEventListener("error", transferFailed); oReq.addEventListener("abort", transferCanceled); oReq.open(); // ... // progress on transfers from the server to the client (downloads) function updateProgress (oEvent) { if (oEvent.lengthComputable) { var percentComplete = oEvent.loaded / oEvent.total * 100; // ... } else { // Unable to compute progress information since the total size is unknown } } function transferComplete(evt) { console.log("The transfer is complete."); } function transferFailed(evt) { console.log("An error occurred while transferring the file."); } function transferCanceled(evt) { console.log("The transfer has been canceled by the user."); }

Lines 3-6 add event listeners for the various events that are sent while performing a data transfer using XMLHttpRequest .

Note: You need to add the event listeners before calling open() on the request. Otherwise the progress events will not fire.

The progress event handler, specified by the updateProgress() function in this example, receives the total number of bytes to transfer as well as the number of bytes transferred so far in the event's total and loaded fields. However, if the lengthComputable field is false, the total length is not known and will be zero.

Progress events exist for both download and upload transfers. The download events are fired on the XMLHttpRequest object itself, as shown in the above sample. The upload events are fired on the XMLHttpRequest.upload object, as shown below:

var oReq = new XMLHttpRequest(); oReq.upload.addEventListener("progress", updateProgress); oReq.upload.addEventListener("load", transferComplete); oReq.upload.addEventListener("error", transferFailed); oReq.upload.addEventListener("abort", transferCanceled); oReq.open();

Note: Progress events are not available for the file: protocol.

Note: Starting in Gecko 9.0, progress events can now be relied upon to come in for every chunk of data received, including the last chunk in cases in which the last packet is received and the connection closed before the progress event is fired. In this case, the progress event is automatically fired when the load event occurs for that packet. This lets you now reliably monitor progress by only watching the "progress" event.

Note: As of Gecko 12.0, if your progress event is called with a responseType of "moz-blob", the value of response is a Blob containing the data received so far.

One can also detect all three load-ending conditions ( abort , load , or error ) using the loadend event:

req.addEventListener("loadend", loadEnd); function loadEnd(e) { console.log("The transfer finished (although we don't know if it succeeded or not)."); }

Note there is no way to be certain, from the information received by the loadend event, as to which condition caused the operation to terminate; however, you can use this to handle tasks that need to be performed in all end-of-transfer scenarios.

Submitting forms and uploading files

Instances of XMLHttpRequest can be used to submit forms in two ways:

using only AJAX

using the FormData API

Using the FormData API is the simplest and fastest, but has the disadvantage that data collected can not be stringified.

Using only AJAX is more complex, but typically more flexible and powerful.

Using nothing but XMLHttpRequest

Submitting forms without the FormData API does not require other APIs for most use cases. The only case where you need an additional API is if you want to upload one or more files, where you use the FileReader API.

A brief introduction to the submit methods

An html <form> can be sent in four ways:

using the POST method and setting the enctype attribute to application/x-www-form-urlencoded (default);

method and setting the attribute to (default); using the POST method and setting the enctype attribute to text/plain ;

method and setting the attribute to ; using the POST method and setting the enctype attribute to multipart/form-data ;

method and setting the attribute to ; using the GET method (in this case the enctype attribute will be ignored).

Now, consider the submission of a form containing only two fields, named foo and baz . If you are using the POST method the server will receive a string similar to one of the following three examples, depending on the encoding type you are using:

Method: POST ; Encoding type: application/x-www-form-urlencoded (default): Content-Type: application/x-www-form-urlencoded foo=bar&baz=The+first+line.%0D%0AThe+second+line.%0D%0A

Method: POST ; Encoding type: text/plain : Content-Type: text/plain foo=bar baz=The first line. The second line.

Method: POST ; Encoding type: multipart/form-data : Content-Type: multipart/form-data; boundary=---------------------------314911788813839 -----------------------------314911788813839 Content-Disposition: form-data; name="foo" bar -----------------------------314911788813839 Content-Disposition: form-data; name="baz" The first line. The second line. -----------------------------314911788813839--

However, if you are using the GET method, a string like the following will be simply added to the URL:

?foo=bar&baz=The%20first%20line.%0AThe%20second%20line.

A little vanilla framework

All these effects are done automatically by the web browser whenever you submit a <form> . If you want to perform the same effects using JavaScript you have to instruct the interpreter about everything. Therefore, how to send forms in pure AJAX is too complex to be explained here in detail. For this reason, here we place a complete (yet didactic) framework, able to use all four ways to submit, and to upload files:

<!doctype html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>Sending forms with pure AJAX – MDN</title> <script type="text/javascript"> "use strict"; /*\ |*| |*| :: XMLHttpRequest.prototype.sendAsBinary() Polyfill :: |*| |*| https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#sendAsBinary() \*/ if (!XMLHttpRequest.prototype.sendAsBinary) { XMLHttpRequest.prototype.sendAsBinary = function(sData) { var nBytes = sData.length, ui8Data = new Uint8Array(nBytes); for (var nIdx = 0; nIdx < nBytes; nIdx++) { ui8Data[nIdx] = sData.charCodeAt(nIdx) & 0xff; } /* send as ArrayBufferView...: */ this.send(ui8Data); /* ...or as ArrayBuffer (legacy)...: this.send(ui8Data.buffer); */ }; } /*\ |*| |*| :: AJAX Form Submit Framework :: |*| |*| https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest/Using_XMLHttpRequest |*| |*| This framework is released under the GNU Public License, version 3 or later. |*| https://www.gnu.org/licenses/gpl-3.0-standalone.html |*| |*| Syntax: |*| |*| AJAXSubmit(HTMLFormElement); \*/ var AJAXSubmit = (function () { function ajaxSuccess () { /* console.log("AJAXSubmit - Success!"); */ console.log(this.responseText); /* you can get the serialized data through the "submittedData" custom property: */ /* console.log(JSON.stringify(this.submittedData)); */ } function submitData (oData) { /* the AJAX request... */ var oAjaxReq = new XMLHttpRequest(); oAjaxReq.submittedData = oData; oAjaxReq.onload = ajaxSuccess; if (oData.technique === 0) { /* method is GET */ oAjaxReq.open("get", oData.receiver.replace(/(?:\?.*)?$/, oData.segments.length > 0 ? "?" + oData.segments.join("&") : ""), true); oAjaxReq.send(null); } else { /* method is POST */ oAjaxReq.open("post", oData.receiver, true); if (oData.technique === 3) { /* enctype is multipart/form-data */ var sBoundary = "---------------------------" + Date.now().toString(16); oAjaxReq.setRequestHeader("Content-Type", "multipart\/form-data; boundary=" + sBoundary); oAjaxReq.sendAsBinary("--" + sBoundary + "\r

" + oData.segments.join("--" + sBoundary + "\r

") + "--" + sBoundary + "--\r

"); } else { /* enctype is application/x-www-form-urlencoded or text/plain */ oAjaxReq.setRequestHeader("Content-Type", oData.contentType); oAjaxReq.send(oData.segments.join(oData.technique === 2 ? "\r

" : "&")); } } } function processStatus (oData) { if (oData.status > 0) { return; } /* the form is now totally serialized! do something before sending it to the server... */ /* doSomething(oData); */ /* console.log("AJAXSubmit - The form is now serialized. Submitting..."); */ submitData (oData); } function pushSegment (oFREvt) { this.owner.segments[this.segmentIdx] += oFREvt.target.result + "\r

"; this.owner.status--; processStatus(this.owner); } function plainEscape (sText) { /* How should I treat a text/plain form encoding? What characters are not allowed? this is what I suppose...: */ /* "4\3\7 - Einstein said E=mc2" ----> "4\\3\\7\ -\ Einstein\ said\ E\=mc2" */ return sText.replace(/[\s\=\\]/g, "\\$&"); } function SubmitRequest (oTarget) { var nFile, sFieldType, oField, oSegmReq, oFile, bIsPost = oTarget.method.toLowerCase() === "post"; /* console.log("AJAXSubmit - Serializing form..."); */ this.contentType = bIsPost && oTarget.enctype ? oTarget.enctype : "application\/x-www-form-urlencoded"; this.technique = bIsPost ? this.contentType === "multipart\/form-data" ? 3 : this.contentType === "text\/plain" ? 2 : 1 : 0; this.receiver = oTarget.action; this.status = 0; this.segments = []; var fFilter = this.technique === 2 ? plainEscape : escape; for (var nItem = 0; nItem < oTarget.elements.length; nItem++) { oField = oTarget.elements[nItem]; if (!oField.hasAttribute("name")) { continue; } sFieldType = oField.nodeName.toUpperCase() === "INPUT" ? oField.getAttribute("type").toUpperCase() : "TEXT"; if (sFieldType === "FILE" && oField.files.length > 0) { if (this.technique === 3) { /* enctype is multipart/form-data */ for (nFile = 0; nFile < oField.files.length; nFile++) { oFile = oField.files[nFile]; oSegmReq = new FileReader(); /* (custom properties:) */ oSegmReq.segmentIdx = this.segments.length; oSegmReq.owner = this; /* (end of custom properties) */ oSegmReq.onload = pushSegment; this.segments.push("Content-Disposition: form-data; name=\"" + oField.name + "\"; filename=\"" + oFile.name + "\"\r

Content-Type: " + oFile.type + "\r

\r

"); this.status++; oSegmReq.readAsBinaryString(oFile); } } else { /* enctype is application/x-www-form-urlencoded or text/plain or method is GET: files will not be sent! */ for (nFile = 0; nFile < oField.files.length; this.segments.push(fFilter(oField.name) + "=" + fFilter(oField.files[nFile++].name))); } } else if ((sFieldType !== "RADIO" && sFieldType !== "CHECKBOX") || oField.checked) { /* NOTE: this will submit _all_ submit buttons. Detecting the correct one is non-trivial. */ /* field type is not FILE or is FILE but is empty */ this.segments.push( this.technique === 3 ? /* enctype is multipart/form-data */ "Content-Disposition: form-data; name=\"" + oField.name + "\"\r

\r

" + oField.value + "\r

" : /* enctype is application/x-www-form-urlencoded or text/plain or method is GET */ fFilter(oField.name) + "=" + fFilter(oField.value) ); } } processStatus(this); } return function (oFormElement) { if (!oFormElement.action) { return; } new SubmitRequest(oFormElement); }; })(); </script> </head> <body> <h1>Sending forms with pure AJAX</h1> <h2>Using the GET method</h2> <form action="register.php" method="get" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Registration example</legend> <p> First name: <input type="text" name="firstname" /><br /> Last name: <input type="text" name="lastname" /> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> <h2>Using the POST method</h2> <h3>Enctype: application/x-www-form-urlencoded (default)</h3> <form action="register.php" method="post" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Registration example</legend> <p> First name: <input type="text" name="firstname" /><br /> Last name: <input type="text" name="lastname" /> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> <h3>Enctype: text/plain</h3> <form action="register.php" method="post" enctype="text/plain" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Registration example</legend> <p> Your name: <input type="text" name="user" /> </p> <p> Your message:<br /> <textarea name="message" cols="40" rows="8"></textarea> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> <h3>Enctype: multipart/form-data</h3> <form action="register.php" method="post" enctype="multipart/form-data" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Upload example</legend> <p> First name: <input type="text" name="firstname" /><br /> Last name: <input type="text" name="lastname" /><br /> Sex: <input id="sex_male" type="radio" name="sex" value="male" /> <label for="sex_male">Male</label> <input id="sex_female" type="radio" name="sex" value="female" /> <label for="sex_female">Female</label><br /> Password: <input type="password" name="secret" /><br /> What do you prefer: <select name="image_type"> <option>Books</option> <option>Cinema</option> <option>TV</option> </select> </p> <p> Post your photos: <input type="file" multiple name="photos[]"> </p> <p> <input id="vehicle_bike" type="checkbox" name="vehicle[]" value="Bike" /> <label for="vehicle_bike">I have a bike</label><br /> <input id="vehicle_car" type="checkbox" name="vehicle[]" value="Car" /> <label for="vehicle_car">I have a car</label> </p> <p> Describe yourself:<br /> <textarea name="description" cols="50" rows="8"></textarea> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> </body> </html>

To test this, create a page named register.php (which is the action attribute of these sample forms), and put the following minimalistic content:

<?php /* register.php */ header("Content-type: text/plain"); /* NOTE: You should never use `print_r()` in production scripts, or otherwise output client-submitted data without sanitizing it first. Failing to sanitize can lead to cross-site scripting vulnerabilities. */ echo ":: data received via GET ::



"; print_r($_GET); echo "



:: Data received via POST ::



"; print_r($_POST); echo "



:: Data received as \"raw\" (text/plain encoding) ::



"; if (isset($HTTP_RAW_POST_DATA)) { echo $HTTP_RAW_POST_DATA; } echo "



:: Files received ::



"; print_r($_FILES);

The syntax to activate this script is simply:

AJAXSubmit(myForm);

Note: This framework uses the an experimental technique. If you do not need to upload binary files, this framework works fine in most browsers. This framework uses the FileReader API to transmit file uploads. This is a recent API and is not implemented in IE9 or below. For this reason, the AJAX-only upload is considered. If you do not need to upload binary files, this framework works fine in most browsers.

Note: The best way to send binary content is via FileReader API. But, since the aim of this script is to work with a FileReader API. As such, the above script makes sense only when you are dealing with small files. If you do not intend to upload binary content, consider instead using the FormData API. The best way to send binary content is via ArrayBuffers or Blobs in conjuncton with the send() method and possibly the readAsArrayBuffer() method of theAPI. But, since the aim of this script is to work with a stringifiable raw data, we used the sendAsBinary() method in conjunction with the readAsBinaryString() method of theAPI. As such, the above script makes sense only when you are dealing with small files. If you do not intend to upload binary content, consider instead using theAPI.

Note: The non-standard sendAsBinary method is considered deprecated as of Gecko 31 (Firefox 31 / Thunderbird 31 / SeaMonkey 2.28) and will be removed soon. The standard send(Blob data) method can be used instead.

Using FormData objects

The FormData constructor lets you compile a set of key/value pairs to send using XMLHttpRequest . Its primary use is in sending form data, but can also be used independently from a form in order to transmit user keyed data. The transmitted data is in the same format the form's submit() method uses to send data, if the form's encoding type were set to "multipart/form-data". FormData objects can be utilized in a number of ways with an XMLHttpRequest . For examples, and explanations of how one can utilize FormData with XMLHttpRequests, see the Using FormData Objects page. For didactic purposes here is a translation of the previous example transformed to use the FormData API. Note the brevity of the code:

<!doctype html> <html> <head> <meta http-equiv="Content-Type" charset="UTF-8" /> <title>Sending forms with FormData – MDN</title> <script> "use strict"; function ajaxSuccess () { console.log(this.responseText); } function AJAXSubmit (oFormElement) { if (!oFormElement.action) { return; } var oReq = new XMLHttpRequest(); oReq.onload = ajaxSuccess; if (oFormElement.method.toLowerCase() === "post") { oReq.open("post", oFormElement.action); oReq.send(new FormData(oFormElement)); } else { var oField, sFieldType, nFile, sSearch = ""; for (var nItem = 0; nItem < oFormElement.elements.length; nItem++) { oField = oFormElement.elements[nItem]; if (!oField.hasAttribute("name")) { continue; } sFieldType = oField.nodeName.toUpperCase() === "INPUT" ? oField.getAttribute("type").toUpperCase() : "TEXT"; if (sFieldType === "FILE") { for (nFile = 0; nFile < oField.files.length; sSearch += "&" + escape(oField.name) + "=" + escape(oField.files[nFile++].name)); } else if ((sFieldType !== "RADIO" && sFieldType !== "CHECKBOX") || oField.checked) { sSearch += "&" + escape(oField.name) + "=" + escape(oField.value); } } oReq.open("get", oFormElement.action.replace(/(?:\?.*)?$/, sSearch.replace(/^&/, "?")), true); oReq.send(null); } } </script> </head> <body> <h1>Sending forms with FormData</h1> <h2>Using the GET method</h2> <form action="register.php" method="get" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Registration example</legend> <p> First name: <input type="text" name="firstname" /><br /> Last name: <input type="text" name="lastname" /> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> <h2>Using the POST method</h2> <h3>Enctype: application/x-www-form-urlencoded (default)</h3> <form action="register.php" method="post" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Registration example</legend> <p> First name: <input type="text" name="firstname" /><br /> Last name: <input type="text" name="lastname" /> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> <h3>Enctype: text/plain</h3> <p>The text/plain encoding is not supported by the FormData API.</p> <h3>Enctype: multipart/form-data</h3> <form action="register.php" method="post" enctype="multipart/form-data" onsubmit="AJAXSubmit(this); return false;"> <fieldset> <legend>Upload example</legend> <p> First name: <input type="text" name="firstname" /><br /> Last name: <input type="text" name="lastname" /><br /> Sex: <input id="sex_male" type="radio" name="sex" value="male" /> <label for="sex_male">Male</label> <input id="sex_female" type="radio" name="sex" value="female" /> <label for="sex_female">Female</label><br /> Password: <input type="password" name="secret" /><br /> What do you prefer: <select name="image_type"> <option>Books</option> <option>Cinema</option> <option>TV</option> </select> </p> <p> Post your photos: <input type="file" multiple name="photos[]"> </p> <p> <input id="vehicle_bike" type="checkbox" name="vehicle[]" value="Bike" /> <label for="vehicle_bike">I have a bike</label><br /> <input id="vehicle_car" type="checkbox" name="vehicle[]" value="Car" /> <label for="vehicle_car">I have a car</label> </p> <p> Describe yourself:<br /> <textarea name="description" cols="50" rows="8"></textarea> </p> <p> <input type="submit" value="Submit" /> </p> </fieldset> </form> </body> </html>

Note: As we said, FormData objects are not stringifiable objects. If you want to stringify a submitted data, use file when you submit a form through the FormData API you do not need to use the FileReader API also: files are automatically loaded and uploaded. As we said,. If you want to stringify a submitted data, use the previous pure-AJAX example . Note also that, although in this example there are some <input> fields,: files are automatically loaded and uploaded.

function getHeaderTime () { console.log(this.getResponseHeader("Last-Modified")); /* A valid GMTString date or null */ } var oReq = new XMLHttpRequest(); oReq.open("HEAD" /* use HEAD if you only need the headers! */, "yourpage.html"); oReq.onload = getHeaderTime; oReq.send();

Let's create two functions:

function getHeaderTime () { var nLastVisit = parseFloat(window.localStorage.getItem('lm_' + this.filepath)); var nLastModif = Date.parse(this.getResponseHeader("Last-Modified")); if (isNaN(nLastVisit) || nLastModif > nLastVisit) { window.localStorage.setItem('lm_' + this.filepath, Date.now()); isFinite(nLastVisit) && this.callback(nLastModif, nLastVisit); } } function ifHasChanged(sURL, fCallback) { var oReq = new XMLHttpRequest(); oReq.open("HEAD" /* use HEAD - we only need the headers! */, sURL); oReq.callback = fCallback; oReq.filepath = sURL; oReq.onload = getHeaderTime; oReq.send(); }

And to test:

/* Let's test the file "yourpage.html"... */ ifHasChanged("yourpage.html", function (nModif, nVisit) { console.log("The page '" + this.filepath + "' has been changed on " + (new Date(nModif)).toLocaleString() + "!"); });

If you want to know if the current page has changed, please read the article about document.lastModified .

Cross-site XMLHttpRequest

Modern browsers support cross-site requests by implementing the Cross-Origin Resource Sharing (CORS) standard. As long as the server is configured to allow requests from your web application's origin, XMLHttpRequest will work. Otherwise, an INVALID_ACCESS_ERR exception is thrown.

Bypassing the cache

A cross-browser compatible approach to bypassing the cache is appending a timestamp to the URL, being sure to include a "?" or "&" as appropriate. For example:

http://foo.com/bar.html -> http://foo.com/bar.html?12345 http://foo.com/bar.html?foobar=baz -> http://foo.com/bar.html?foobar=baz&12345

As the local cache is indexed by URL, this causes every request to be unique, thereby bypassing the cache.

You can automatically adjust URLs using the following code:

var oReq = new XMLHttpRequest(); oReq.open("GET", url + ((/\?/).test(url) ? "&" : "?") + (new Date()).getTime()); oReq.send(null);

Security

Firefox 3 note Versions of Firefox prior to Firefox 3 allowed you to set the preference capability.policy.<policyname>.XMLHttpRequest.open</policyname> to allAccess to give specific sites cross-site access. This is no longer supported.

Firefox 5 note Versions of Firefox prior to Firefox 5 could use netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead"); to request cross-site access. This is no longer supported, even though it produces no warning and permission dialog is still presented.

The recommended way to enable cross-site scripting is to use the Access-Control-Allow-Origin HTTP header in the response to the XMLHttpRequest.

XMLHttpRequests being stopped

If you conclude with an XMLHttpRequest receiving status=0 and statusText=null , this means the request was not allowed to be performed. It was UNSENT . A likely cause for this is when the XMLHttpRequest origin (at the creation of the XMLHttpRequest) has changed when the XMLHttpRequest is subsequently open() . This case can happen, for example, when one has an XMLHttpRequest that gets fired on an onunload event for a window, the expected XMLHttpRequest is created when the window to be closed is still there, and finally sending the request (in otherwords, open() ) when this window has lost its focus and another window gains focus. The most effective way to avoid this problem is to set a listener on the new window's activate event which is set once the terminated window has its unload event triggered.

Workers

Setting overrideMimeType does not work from a Worker . See bug 678057 for more details. Other browsers may handle this differently.

Specifications

Specification Status Comment XMLHttpRequest Living Standard Live standard, latest version

Browser compatibility

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub Desktop Mobile Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet XMLHttpRequest Chrome Full support 1 Edge Full support 12 Full support 12 No support 12 — 79 Notes Notes Implemented via ActiveXObject('Microsoft.XMLHTTP') Firefox Full support 1 IE Full support 7 Full support 7 Full support 5 Notes Notes Implemented via ActiveXObject('Microsoft.XMLHTTP') Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 abort Chrome Full support 18 Edge Full support 12 Firefox Full support Yes IE Full support 5 Opera Full support Yes Safari Full support 1.2 WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support Yes abort event Chrome Full support Yes Edge Full support ≤79 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS ? Samsung Internet Android Full support Yes error event Chrome Full support Yes Edge Full support ≤79 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS ? Samsung Internet Android Full support Yes getAllResponseHeaders Chrome Full support 1 Edge Full support 12 Firefox Full support 4 Notes Full support 4 Notes Notes Starting from Firefox 49, empty headers are returned as empty strings in case the preference network.http.keep_empty_response_headers_as_empty_string is set to true , defaulting to false . Before Firefox 49 empty headers had been ignored. Since Firefox 50 the preference defaults to true . IE Full support 5 Opera Full support Yes Safari Full support 1.2 WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support 4 Notes Full support 4 Notes Notes Starting from Firefox 49, empty headers are returned as empty strings in case the preference network.http.keep_empty_response_headers_as_empty_string is set to true , defaulting to false . Before Firefox 49 empty headers had been ignored. Since Firefox 50 the preference defaults to true . Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support Yes getResponseHeader Chrome Full support 1 Edge Full support 12 Firefox Full support 1 Notes Full support 1 Notes Notes Starting from Firefox 49, empty headers are returned as empty strings in case the preference network.http.keep_empty_response_headers_as_empty_string is set to true , defaulting to false . Before Firefox 49 empty headers had been ignored. Since Firefox 50 the preference defaults to true . IE Full support 5 Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Notes Full support 4 Notes Notes Starting from Firefox 49, empty headers are returned as empty strings in case the preference network.http.keep_empty_response_headers_as_empty_string is set to true , defaulting to false . Before Firefox 49 empty headers had been ignored. Since Firefox 50 the preference defaults to true . Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 load event Chrome Full support Yes Edge Full support ≤79 Firefox Full support Yes IE Full support 9 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS ? Samsung Internet Android Full support Yes loadend event Chrome Full support Yes Edge Full support ≤79 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS ? Samsung Internet Android Full support Yes loadstart event Chrome Full support Yes Edge Full support ≤79 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS ? Samsung Internet Android Full support Yes onreadystatechange Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 5 Opera Full support 9 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 open Chrome Full support 1 Edge Full support 12 Firefox Full support 1 Notes Full support 1 Notes Notes Starting in Firefox 30, synchronous requests on the main thread have been deprecated due to their negative impact on performance and the user experience. Therefore, the async parameter may not be false except in a Worker . IE Full support 5 Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Notes Full support 4 Notes Notes Starting in Firefox 30, synchronous requests on the main thread have been deprecated due to their negative impact on performance and the user experience. Therefore, the async parameter may not be false except in a Worker . Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 overrideMimeType Chrome Full support 1 Edge Full support 12 Firefox Full support Yes IE Full support 11 Full support 11 Full support 5 Notes Notes Implemented via ActiveXObject Opera Full support Yes Safari Full support 1.2 WebView Android Full support Yes Chrome Android Full support 18 Firefox Android Full support Yes Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support 1.0 progress event Chrome Full support Yes Edge Full support ≤79 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS ? Samsung Internet Android Full support Yes readyState Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 7 Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 response Chrome Full support 9 Edge Full support 12 Firefox Full support 6 IE Full support 10 Opera Full support 11.6 Safari Full support 5.1 WebView Android Full support ≤37 Chrome Android Full support 18 Firefox Android Full support 6 Opera Android Full support 12 Safari iOS Full support 6 Samsung Internet Android Full support 1.0 responseText Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 5 Notes Full support 5 Notes Notes Before Internet Explorer 10, the value of XMLHttpRequest.responseText could be read only once the request was complete. Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 responseType Chrome Full support 31 Edge Full support 12 Firefox Full support 6 IE Full support 10 Opera Full support 18 Safari Full support 7 WebView Android Full support 55 Chrome Android Full support 55 Firefox Android Full support 50 Opera Android Full support 42 Safari iOS Full support 7 Samsung Internet Android Full support 6.0 responseURL Chrome Full support 37 Edge Full support 14 Firefox Full support 32 IE No support No Opera Full support 24 Safari Full support 8 WebView Android Full support 37 Chrome Android Full support 37 Firefox Android Full support 32 Opera Android Full support 24 Safari iOS Full support Yes Samsung Internet Android Full support 3.0 responseXML Chrome Full support Yes Edge Full support 12 Firefox Full support Yes Notes Full support Yes Notes Notes Prior to Firefox 51, an error parsing the received data added a <parsererror> node to the top of the Document and then returned the Document in whatever state it happens to be in. This was inconsistent with the specification. Starting with Firefox 51, this scenario now correctly returns null as per the spec. IE Full support Yes Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Notes Full support Yes Notes Notes Prior to Firefox 51, an error parsing the received data added a <parsererror> node to the top of the Document and then returned the Document in whatever state it happens to be in. This was inconsistent with the specification. Starting with Firefox 51, this scenario now correctly returns null as per the spec. Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support Yes send Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 5 Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 sendAsBinary Deprecated Non-standard Chrome No support No Notes No support No Notes Notes There is a polyfill available to support sendAsBinary() . Edge No support No Notes No support No Notes Notes There is a polyfill available to support sendAsBinary() . Firefox No support 2 — 31 IE No support No Opera No support No Safari No support No WebView Android No support No Notes No support No Notes Notes There is a polyfill available to support sendAsBinary() . Chrome Android No support No Notes No support No Notes Notes There is a polyfill available to support sendAsBinary() . Firefox Android No support 4 — 31 Opera Android No support No Safari iOS No support No Samsung Internet Android No support No Notes No support No Notes Notes There is a polyfill available to support sendAsBinary() . setRequestHeader Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 5 Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 status Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 7 Notes Full support 7 Notes Notes Internet Explorer version 5 and 6 supported ajax calls using ActiveXObject() Opera Full support 8 Safari Full support 1.2 WebView Android Full support 1 Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support 10.1 Safari iOS Full support 1 Samsung Internet Android Full support 1.0 statusText Chrome Full support 1 Edge Full support 12 Firefox Full support 1 IE Full support 7 Notes Full support 7 Notes Notes Internet Explorer version 5 and 6 supported ajax calls using ActiveXObject() Opera Full support Yes Safari Full support 1.2 WebView Android Full support Yes Chrome Android Full support 18 Firefox Android Full support 4 Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support 1.0 timeout Chrome Full support 29 Edge Full support 12 Firefox Full support 12 IE Full support 8 Opera Full support 17 Full support 17 No support 12 — 16 Safari Full support 6.1 WebView Android Full support ≤37 Chrome Android Full support 29 Firefox Android Full support 14 Opera Android Full support 18 Full support 18 No support 12 — 16 Safari iOS Full support 7 Samsung Internet Android Full support 2.0 timeout event Chrome Full support Yes Edge Full support ≤18 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support Yes Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support Yes upload Chrome Full support 1 Edge Full support 12 Firefox Full support Yes IE Full support 10 Opera Full support Yes Safari Full support 10 WebView Android Full support Yes Chrome Android Full support 18 Firefox Android Full support Yes Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support 1.0 withCredentials Chrome Full support 3 Edge Full support 12 Firefox Full support 3.5 Notes Full support 3.5 Notes Notes Starting with Firefox 11, it's no longer supported to use the withCredentials attribute when performing synchronous requests. Attempting to do so throws an NS_ERROR_DOM_INVALID_ACCESS_ERR exception. IE Full support 10 Notes Full support 10 Notes Notes Internet Explorer versions 8 and 9 supported cross-domain requests (CORS) using XDomainRequest . Opera Full support 12 Safari Full support 4 WebView Android Full support ≤37 Chrome Android Full support 18 Firefox Android Full support 4 Notes Full support 4 Notes Notes Starting with Firefox 11, it's no longer supported to use the withCredentials attribute when performing synchronous requests. Attempting to do so throws an NS_ERROR_DOM_INVALID_ACCESS_ERR exception. Opera Android Full support 12 Safari iOS Full support 3.2 Samsung Internet Android Full support 1.0 Legend Full support Full support No support No support Compatibility unknown Compatibility unknown Non-standard. Expect poor cross-browser support. Non-standard. Expect poor cross-browser support. Deprecated. Not for use in new websites. Deprecated. Not for use in new websites. See implementation notes. See implementation notes.

See also