jQuery.ajax()
jQuery.ajax( url [, settings] ) Returns: jqXHR
Description: Perform an asynchronous HTTP (Ajax) request.
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version added: 1.5jQuery.ajax( url [, settings] )
urlA string containing the URL to which the request is sent.
settingsA set of key/value pairs that configure the Ajax request. All settings are optional. A default can be set for any option with $.ajaxSetup(). See jQuery.ajax( settings ) below for a complete list of all settings.
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version added: 1.0jQuery.ajax( settings )
settingsA set of key/value pairs that configure the Ajax request. All settings are optional. A default can be set for any option with $.ajaxSetup().
The $.ajax() function underlies all Ajax requests sent by jQuery. It is often unnecessary to directly call this function, as several higher-level alternatives like $.get() and .load() are available and are easier to use. If less common options are required, though, $.ajax() can be used more flexibly.
At its simplest, the $.ajax() function can be called with no arguments:
$.ajax();
Note: Default settings can be set globally by using the $.ajaxSetup() function.
This example, using no options, loads the contents of the current page, but does nothing with the result. To use the result, we can implement one of the callback functions.
The jqXHR Object
The jQuery XMLHttpRequest (jqXHR) object returned by $.ajax() as of jQuery 1.5 is a superset of the browser's native XMLHttpRequest object. For example, it contains responseText and responseXML properties, as well as a getResponseHeader() method. When the transport mechanism is something other than XMLHttpRequest (for example, a script tag for a JSONP request) the jqXHR object simulates native XHR functionality where possible.
As of jQuery 1.5.1, the jqXHR object also contains the overrideMimeType() method (it was available in jQuery 1.4.x, as well, but was temporarily removed in jQuery 1.5). The .overrideMimeType() method may be used in the beforeSend() callback function, for example, to modify the response content-type header:
$.ajax({
url: 'http://fiddle.jshell.net/favicon.png',
beforeSend: function( xhr ) {
xhr.overrideMimeType( 'text/plain; charset=x-user-defined' );
},
success: function( data ) {
if (console && console.log){
console.log( 'Sample of data:', data.slice(0,100) );
}
}
});
The jqXHR objects returned by $.ajax() as of jQuery 1.5 implement the Promise interface, giving them all the properties, methods, and behavior of a Promise (see Deferred object for more information). For convenience and consistency with the callback names used by $.ajax(), jqXHR also provides .error(), .success(), and .complete() methods. These methods take a function argument that is called when the $.ajax() request terminates, and the function receives the same arguments as the correspondingly-named $.ajax() callback. This allows you to assign multiple callbacks on a single request, and even to assign callbacks after the request may have completed. (If the request is already complete, the callback is fired immediately.)
Deprecation Notice: The
jqXHR.success(),jqXHR.error(), andjqXHR.complete()callbacks will be deprecated in jQuery 1.8. To prepare your code for their eventual removal, usejqXHR.done(),jqXHR.fail(), andjqXHR.always()instead.
// Assign handlers immediately after making the request,
// and remember the jqxhr object for this request
var jqxhr = $.ajax( "example.php" )
.done(function() { alert("success"); })
.fail(function() { alert("error"); })
.always(function() { alert("complete"); });
// perform other work here ...
// Set another completion function for the request above
jqxhr.always(function() { alert("second complete"); });
For backward compatibility with XMLHttpRequest, a jqXHR object will expose the following properties and methods:
readyStatestatusstatusText-
responseXMLand/orresponseTextwhen the underlying request responded with xml and/or text, respectively -
setRequestHeader(name, value)which departs from the standard by replacing the old value with the new one rather than concatenating the new value to the old one getAllResponseHeaders()getResponseHeader()abort()
No onreadystatechange mechanism is provided, however, since success, error, complete and statusCode cover all conceivable requirements.
Callback Function Queues
The beforeSend, error, dataFilter, success and complete options all accept callback functions that are invoked at the appropriate times.
As of jQuery 1.5, the error (fail), success (done), and complete (always, as of jQuery 1.6) callback hooks are first-in, first-out managed queues. This means you can assign more than one callback for each hook. See Deferred object methods, which are implemented internally for these $.ajax() callback hooks.
The this reference within all callbacks is the object in the context option passed to $.ajax in the settings; if context is not specified, this is a reference to the Ajax settings themselves.
Some types of Ajax requests, such as JSONP and cross-domain GET requests, do not use XHR; in those cases the XMLHttpRequest and textStatus parameters passed to the callback are undefined.
Here are the callback hooks provided by $.ajax():
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beforeSendcallback is invoked; it receives thejqXHRobject and thesettingsmap as parameters. -
errorcallbacks are invoked, in the order they are registered, if the request fails. They receive thejqXHR, a string indicating the error type, and an exception object if applicable. Some built-in errors will provide a string as the exception object: "abort", "timeout", "No Transport". -
dataFiltercallback is invoked immediately upon successful receipt of response data. It receives the returned data and the value ofdataType, and must return the (possibly altered) data to pass on tosuccess. -
successcallbacks are then invoked, in the order they are registered, if the request succeeds. They receive the returned data, a string containing the success code, and thejqXHRobject. -
completecallbacks fire, in the order they are registered, when the request finishes, whether in failure or success. They receive thejqXHRobject, as well as a string containing the success or error code.
For example, to make use of the returned HTML, we can implement a success handler:
$.ajax({
url: 'ajax/test.html',
success: function(data) {
$('.result').html(data);
alert('Load was performed.');
}
});
Data Types
The $.ajax() function relies on the server to provide information about the retrieved data. If the server reports the return data as XML, the result can be traversed using normal XML methods or jQuery's selectors. If another type is detected, such as HTML in the example above, the data is treated as text.
Different data handling can be achieved by using the dataType option. Besides plain xml, the dataType can be html, json, jsonp, script, or text.
The text and xml types return the data with no processing. The data is simply passed on to the success handler, either through the responseText or responseXML property of the jqXHR object, respectively.
Note: We must ensure that the MIME type reported by the web server matches our choice of dataType. In particular, XML must be declared by the server as text/xml or application/xml for consistent results.
If html is specified, any embedded JavaScript inside the retrieved data is executed before the HTML is returned as a string. Similarly, script will execute the JavaScript that is pulled back from the server, then return nothing.
The json type parses the fetched data file as a JavaScript object and returns the constructed object as the result data. To do so, it uses jQuery.parseJSON() when the browser supports it; otherwise it uses a Function constructor. Malformed JSON data will throw a parse error (see json.org for more information). JSON data is convenient for communicating structured data in a way that is concise and easy for JavaScript to parse. If the fetched data file exists on a remote server, specify the jsonp type instead.
The jsonp type appends a query string parameter of callback=? to the URL. The server should prepend the JSON data with the callback name to form a valid JSONP response. We can specify a parameter name other than callback with the jsonp option to $.ajax().
Note: JSONP is an extension of the JSON format, requiring some server-side code to detect and handle the query string parameter. More information about it can be found in the original post detailing its use.
When data is retrieved from remote servers (which is only possible using the script or jsonp data types), the error callbacks and global events will never be fired.
Sending Data to the Server
By default, Ajax requests are sent using the GET HTTP method. If the POST method is required, the method can be specified by setting a value for the type option. This option affects how the contents of the data option are sent to the server. POST data will always be transmitted to the server using UTF-8 charset, per the W3C XMLHTTPRequest standard.
The data option can contain either a query string of the form key1=value1&key2=value2, or a map of the form {key1: 'value1', key2: 'value2'}. If the latter form is used, the data is converted into a query string using jQuery.param() before it is sent. This processing can be circumvented by setting processData to false. The processing might be undesirable if you wish to send an XML object to the server; in this case, change the contentType option from application/x-www-form-urlencoded to a more appropriate MIME type.
Advanced Options
The global option prevents handlers registered using .ajaxSend(), .ajaxError(), and similar methods from firing when this request would trigger them. This can be useful to, for example, suppress a loading indicator that was implemented with .ajaxSend() if the requests are frequent and brief. With cross-domain script and JSONP requests, the global option is automatically set to false. See the descriptions of these methods below for more details. See the descriptions of these methods below for more details.
If the server performs HTTP authentication before providing a response, the user name and password pair can be sent via the username and password options.
Ajax requests are time-limited, so errors can be caught and handled to provide a better user experience. Request timeouts are usually either left at their default or set as a global default using $.ajaxSetup() rather than being overridden for specific requests with the timeout option.
By default, requests are always issued, but the browser may serve results out of its cache. To disallow use of the cached results, set cache to false. To cause the request to report failure if the asset has not been modified since the last request, set ifModified to true.
The scriptCharset allows the character set to be explicitly specified for requests that use a <script> tag (that is, a type of script or jsonp). This is useful if the script and host page have differing character sets.
The first letter in Ajax stands for "asynchronous," meaning that the operation occurs in parallel and the order of completion is not guaranteed. The async option to $.ajax() defaults to true, indicating that code execution can continue after the request is made. Setting this option to false (and thus making the call no longer asynchronous) is strongly discouraged, as it can cause the browser to become unresponsive.
The $.ajax() function returns the XMLHttpRequest object that it creates. Normally jQuery handles the creation of this object internally, but a custom function for manufacturing one can be specified using the xhr option. The returned object can generally be discarded, but does provide a lower-level interface for observing and manipulating the request. In particular, calling .abort() on the object will halt the request before it completes.
At present, due to a bug in Firefox where .getAllResponseHeaders() returns the empty string although .getResponseHeader('Content-Type') returns a non-empty string, automatically decoding JSON CORS responses in Firefox with jQuery is not supported.
A workaround to this is possible by overriding jQuery.ajaxSettings.xhr as follows:
var _super = jQuery.ajaxSettings.xhr;
jQuery.ajaxSettings.xhr = function () {
var xhr = _super(),
getAllResponseHeaders = xhr.getAllResponseHeaders;
xhr.getAllResponseHeaders = function () {
if ( getAllResponseHeaders() ) {
return getAllResponseHeaders();
}
var allHeaders = "";
$( ["Cache-Control", "Content-Language", "Content-Type",
"Expires", "Last-Modified", "Pragma"] ).each(function (i, header_name) {
if ( xhr.getResponseHeader( header_name ) ) {
allHeaders += header_name + ": " + xhr.getResponseHeader( header_name ) + "\n";
}
return allHeaders;
});
};
return xhr;
};
Extending Ajax
As of jQuery 1.5, jQuery's Ajax implementation includes prefilters, converters, and transports that allow you to extend Ajax with a great deal of flexibility. For more information about these advanced features, see the Extending Ajax page.
Additional Notes:
- Due to browser security restrictions, most "Ajax" requests are subject to the same origin policy; the request can not successfully retrieve data from a different domain, subdomain, or protocol.
- Script and JSONP requests are not subject to the same origin policy restrictions.
Examples:
Example: Save some data to the server and notify the user once it's complete.
$.ajax({
type: "POST",
url: "some.php",
data: "name=John&location=Boston"
}).done(function( msg ) {
alert( "Data Saved: " + msg );
});Example: Retrieve the latest version of an HTML page.
$.ajax({
url: "test.html",
cache: false,
success: function(html){
$("#results").append(html);
}
});Example: Send an xml document as data to the server. By setting the processData option to false, the automatic conversion of data to strings is prevented.
var xmlDocument = [create xml document];
var xmlRequest = $.ajax({
url: "page.php",
processData: false,
data: xmlDocument
});
xmlRequest.done(handleResponse);Example: Send an id as data to the server, save some data to the server, and notify the user once it's complete. If the request fails, alert the user.
var menuId = $("ul.nav").first().attr("id");
var request = $.ajax({
url: "script.php",
type: "POST",
data: {id : menuId},
dataType: "html"
});
request.done(function(msg) {
$("#log").html( msg );
});
request.fail(function(jqXHR, textStatus) {
alert( "Request failed: " + textStatus );
});Example: Load and execute a JavaScript file.
$.ajax({
type: "GET",
url: "test.js",
dataType: "script"
});