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:
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, you 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:
1 2 3 4 5 6 7 8 9 10 11 | url: "http://fiddle.jshell.net/favicon.png",
beforeSend: function( xhr ) {
xhr.overrideMimeType( "text/plain; charset=x-user-defined" );
if ( console && console.log ) {
console.log( "Sample of data:", data.slice( 0, 100 ) );
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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). These methods take one or more function arguments that are called when the $.ajax()
request terminates. 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.) Available Promise methods of the jqXHR object include:
- jqXHR.done(function( data, textStatus, jqXHR ) {});
An alternative construct to the success callback option, the .done()
method replaces the deprecated jqXHR.success()
method. Refer to deferred.done()
for implementation details.
- jqXHR.fail(function( jqXHR, textStatus, errorThrown ) {});
An alternative construct to the error callback option, the .fail()
method replaces the deprecated .error()
method. Refer to deferred.fail()
for implementation details.
- jqXHR.always(function( data|jqXHR, textStatus, jqXHR|errorThrown ) { });
An alternative construct to the complete callback option, the .always()
method replaces the deprecated .complete()
method.
In response to a successful request, the function's arguments are the same as those of .done()
: data, textStatus, and the jqXHR object. For failed requests the arguments are the same as those of .fail()
: the jqXHR object, textStatus, and errorThrown. Refer to deferred.always()
for implementation details.
- jqXHR.then(function( data, textStatus, jqXHR ) {}, function( jqXHR, textStatus, errorThrown ) {});
Incorporates the functionality of the .done()
and .fail()
methods, allowing (as of jQuery 1.8) the underlying Promise to be manipulated. Refer to deferred.then()
for implementation details.
Deprecation Notice: The jqXHR.success()
, jqXHR.error()
, and jqXHR.complete()
callbacks are deprecated as of jQuery 1.8. To prepare your code for their eventual removal, use jqXHR.done()
, jqXHR.fail()
, and jqXHR.always()
instead.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | var jqxhr = $.ajax( "example.php" )
jqxhr.always(function() {
alert( "second complete" );
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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.
For backward compatibility with XMLHttpRequest
, a jqXHR
object will expose the following properties and methods:
readyState
status
statusText
responseXML
and/or responseText
when the underlying request responded with xml and/or text, respectivelysetRequestHeader(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 onegetAllResponseHeaders()
getResponseHeader()
statusCode()
abort()
No onreadystatechange
mechanism is provided, however, since done
, fail
, always
, 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 fail
and done
, and, as of jQuery 1.6, always
callback hooks are first-in, first-out managed queues, allowing for more than one callback for each hook. See Deferred object methods, which are implemented internally for these $.ajax()
callback hooks.
The callback hooks provided by $.ajax()
are as follows:
beforeSend
callback option is invoked; it receives the jqXHR
object and the settings
object as parameters.error
callback option is invoked, if the request fails. It receives the jqXHR
, 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".dataFilter
callback option is invoked immediately upon successful receipt of response data. It receives the returned data and the value of dataType
, and must return the (possibly altered) data to pass on to success
.success
callback option is invoked, if the request succeeds. It receives the returned data, a string containing the success code, and the jqXHR
object.- Promise callbacks —
.done()
, .fail()
, .always()
, and .then()
— are invoked, in the order they are registered. complete
callback option fires, when the request finishes, whether in failure or success. It receives the jqXHR
object, as well as a string containing the success or error code.
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 an object 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.
Extending Ajax
As of jQuery 1.5, jQuery's Ajax implementation includes prefilters, transports, and converters that allow you to extend Ajax with a great deal of flexibility.
Using Converters
$.ajax()
converters support mapping data types to other data types. If, however, you want to map a custom data type to a known type (e.g json
), you must add a correspondance between the response Content-Type and the actual data type using the contents
option:
1 2 3 4 5 6 7 8 9 10 11 | mycustomtype: /mycustomtype/
"mycustomtype json": function( result ) {
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This extra object is necessary because the response Content-Types and data types never have a strict one-to-one correspondance (hence the regular expression).
To convert from a supported type (e.g text
, json
) to a custom data type and back again, use another pass-through converter:
1 2 3 4 5 6 7 8 9 10 11 12 | mycustomtype: /mycustomtype/
"text mycustomtype": true,
"mycustomtype json": function( result ) {
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The above now allows passing from text
to mycustomtype
and then mycustomtype
to json
.