Contents
  1. 1. jQuery Ajax Basic
    1. 1.1. Ajax Requests
    2. 1.2. Ajax Settings
      1. 1.2.1. Settings for Request
      2. 1.2.2. Settings for Response
      3. 1.2.3. Settings for Ajax Event
      4. 1.2.4. Settings for Global Ajax Event
    3. 1.3. The jqXHR Object
      1. 1.3.1. overrideMimeType()
      2. 1.3.2. Promise interface
    4. 1.4. Data Type
    5. 1.5. Sending Data to the Server
    6. 1.6. Additional Notes
  2. 2. Global Ajax Event Handlers
  3. 3. Helper Functions
  4. 4. Low-Level Interface
  5. 5. Shorthand Methods
  6. 6. Summary
  7. 7. References

jQuery Ajax Basic

Ajax Requests

jQuery.ajax(url [, settings ]) or jQuery.ajax( [settings] )

Perform an asynchronous HTTP (Ajax) request.

  • $.ajax()
  • $.get()
  • $.post()
  • $.load()

jQuery.ajaxSetup(options)

Set default values for future Ajax requests. Its use is not recommended.

options: A set of key/value pairs that configure the default Ajax request. All options are optional.

All subsequent Ajax calls using any function will use the new settings, unless overridden by the individual calls, until the next invocation of $.ajaxSetup().

Note: The settings specified here will affect all calls to $.ajax or Ajax-based derivatives such as $.get(). This can cause undesirable behavior since other callers (for example, plugins) may be expecting the normal default settings. For that reason we strongly recommend against using this API. Instead, set the options explicitly in the call or define a simple plugin to do so.

For example: Sets the defaults for Ajax requests to the url “/xmlhttp/“, disables global handlers and uses POST instead of GET. The following Ajax requests then sends some data without having to set anything else.

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$.ajaxSetup({
url: "/xmlhttp/",
global: false,
type: "POST"
});
$.ajax({ data: myData });

Ajax Settings

settings

  • Type: PlainObject

A set of key/value pairs that configure the Ajax request. All settings are optional. A default can be set for any option with $.ajaxSetup()

Settings for Request

accepts

  • Type: PlainObject
  • default: depends on dataType

A set of key/value pairs that map a given dataType to its MIME type, which gets sent in the Accept request header. This header tells the server what kind of response it will accept in return.

async

  • Type: Boolean
  • default: true

By default, all requests are sent asynchronously (i.e. this is set to true by default). If you need synchronous requests, set this option to false. Cross-domain requests and dataType: "jsonp" requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active.

cache

  • Type: Boolean
  • Default: true, false for dataType 'script' and 'jsonp'

If set to false, it will force requested pages not to be cached by the browser.

Retrieve the latest version of an HTML page.

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$.ajax({
url: "test.html",
cache: false
})
.done(function( html ) {
$( "#results" ).append( html );
});

contentType

  • Type: Boolean or String
  • Default: 'application/x-www-form-urlencoded; charset=UTF-8'

When sending data to the server, use this content type. Default is “application/x-www-form-urlencoded; charset=UTF-8”, which is fine for most cases. If you explicitly pass in a content-type to $.ajax(), then it is always sent to the server (even if no data is sent). As of jQuery 1.6 you can pass false to tell jQuery to not set any content type header. Note: The W3C XMLHttpRequest specification dictates that the charset is always UTF-8; specifying another charset will not force the browser to change the encoding. Note: For cross-domain requests, setting the content type to anything other than application/x-www-form-urlencoded, multipart/form-data, or text/plain will trigger the browser to send a preflight OPTIONS request to the server.

crossDomain

  • Type: Boolean
  • Default: false for same-domain requests, true for cross-domain requests

If you wish to force a crossDomain request (such as JSONP) on the same domain, set the value of crossDomain to true. This allows, for example, server-side redirection to another domain. (version added: 1.5)

data

  • Type: PlainObject or String or Array

Data to be sent to the server. If the HTTP method is one that cannot have an entity body, such as GET, the data is appended to the URL.

When data is an object, jQuery generates the data string from the object’s key/value pairs unless the processData option is set to false. For example, { a: "bc", d: "e,f" } is converted to the string "a=bc&d=e%2Cf". If the value is an array, jQuery serializes multiple values with same key based on the value of the traditional setting (described below). For example, { a: [1,2] } becomes the string "a%5B%5D=1&a%5B%5D=2" with the default traditional: false setting.

When data is passed as a string it should already be encoded using the correct encoding for contentType, which by default is application/x-www-form-urlencoded.

In requests with dataType: "json" or dataType: "jsonp", if the string contains a double question mark (??) anywhere in the URL or a single question mark (?) in the query string, it is replaced with a value generated by jQuery that is unique for each copy of the library on the page (e.g. jQuery21406515378922229067_1479880736745).

dataType

  • Type: String
  • Default: Intelligent Guess (xml, json, script, or html)
  • values: “xml”, “html”, “script”, “json”, “jsonp”, “text”

The type of data that you’re expecting back from the server. If none is specified, jQuery will try to infer it based on the MIME type of the response.

multiple, space-separated values: As of jQuery 1.5, jQuery can convert a dataType from what it received in the Content-Type header to what you require. For example, if you want a text response to be treated as XML, use "text xml" for the dataType.

headers

  • Type: PlainObject
  • default: {}

An object of additional header key/value pairs to send along with requests using the XMLHttpRequest transport. The header X-Requested-With: XMLHttpRequest is always added, but its default XMLHttpRequest value can be changed here. Values in the headers setting can also be overwritten from within the beforeSend function. (version added: 1.5)

ifModified

  • Type: Boolean
  • Default: false

Allow the request to be successful only if the response has changed since the last request. This is done by checking the Last-Modified header. Default value is false, ignoring the header. In jQuery 1.4 this technique also checks the ‘etag’ specified by the server to catch unmodified data.

isLocal

  • Type: Boolean
  • Default: depends on current location protocol

Allow the current environment to be recognized as “local,” (e.g. the filesystem), even if jQuery does not recognize it as such by default. The following protocols are currently recognized as local: file, *-extension, and widget. If the isLocal setting needs modification, it is recommended to do so once in the $.ajaxSetup() method. (version added: 1.5.1)

jsonp

  • Type: String or Boolean

Override the callback function name in a JSONP request. This value will be used instead of ‘callback’ in the ‘callback=?’ part of the query string in the url. So {jsonp:’onJSONPLoad’} would result in ‘onJSONPLoad=?’ passed to the server. As of jQuery 1.5, setting the jsonp option to false prevents jQuery from adding the “?callback” string to the URL or attempting to use “=?” for transformation. In this case, you should also explicitly set the jsonpCallback setting. For example, { jsonp: false, jsonpCallback: “callbackName” }. If you don’t trust the target of your Ajax requests, consider setting the jsonp property to false for security reasons.

jsonpCallback

  • Type: String or Function()

Specify the callback function name for a JSONP request. This value will be used instead of the random name automatically generated by jQuery.

method

  • Type: String
  • Default: 'GET'

mimeType

  • Type: String

A mime type to override the XHR mime type.

password

  • Type: String

A password to be used with XMLHttpRequest in response to an HTTP access authentication request.

processData

  • Type: Boolean
  • Default: true

By default, data passed in to the data option as an object (technically, anything other than a string) will be processed and transformed into a query string, fitting to the default content-type “application/x-www-form-urlencoded”. If you want to send a DOMDocument, or other non-processed data, set this option to false.

scriptAttrs

  • Type: PlainObject

Defines an object with additional attributes to be used in a “script” or “jsonp” request. The key represents the name of the attribute and the value is the attribute’s value. If this object is provided it will force the use of a script-tag transport. For example, this can be used to set nonce, integrity, or crossorigin attributes to satisfy Content Security Policy requirements. (version added: 3.4.0)

scriptCharset

  • Type: String

Only applies when the “script” transport is used. Sets the charset attribute on the script tag used in the request. Used when the character set on the local page is not the same as the one on the remote script. Alternatively, the charset attribute can be specified in scriptAttrs instead, which will also ensure the use of the “script” transport.

timeout

  • Type: Number

Set a timeout (in milliseconds) for the request. A value of 0 means there will be no timeout. This will override any global timeout set with $.ajaxSetup(). The timeout period starts at the point the $.ajax call is made; if several other requests are in progress and the browser has no connections available, it is possible for a request to time out before it can be sent.

traditional

  • Type: Boolean

Set this to true if you wish to use the traditional style of param serialization.

traditional=true, param is encoded, traditional=false, params is decoded

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var myObject = {
a: {
one: 1,
two: 2,
three: 3
},
b: [ 1, 2, 3 ]
};
var recursiveEncoded = $.param( myObject );
var recursiveDecoded = decodeURIComponent( $.param( myObject ) );
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a%5Bone%5D=1&a%5Btwo%5D=2&a%5Bthree%5D=3&b%5B%5D=1&b%5B%5D=2&b%5B%5D=3
a[one]=1&a[two]=2&a[three]=3&b[]=1&b[]=2&b[]=3

type

  • Type: String
  • Default: ‘GET’

An alias for method. You should use type if you’re using versions of jQuery prior to 1.9.0.

url

  • Type: String
  • Default: The current page

A string containing the URL to which the request is sent.

username

  • Type: String

A username to be used with XMLHttpRequest in response to an HTTP access authentication request.

xhr

  • Type: Function()
  • default: ActiveXObject when available (IE), the XMLHttpRequest otherwise

Callback for creating the XMLHttpRequest object. Defaults to the ActiveXObject when available (IE), the XMLHttpRequest otherwise. Override to provide your own implementation for XMLHttpRequest or enhancements to the factory.

xhrFields

  • Type: PlainObject

An object of fieldName-fieldValue pairs to set on the native XHR object. For example, you can use it to set withCredentials to true for cross-domain requests if needed.

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$.ajax({
url: a_cross_domain_url,
xhrFields: {
withCredentials: true
}
});

Settings for Response

contents

  • Type: PlainObject

An object of string/regular-expression pairs that determine how jQuery will parse the response, given its content type. (version added: 1.5)

context

  • Type: PlainObject

This object will be the context of all Ajax-related callbacks. By default, the context is an object that represents the Ajax settings used in the call ($.ajaxSettings merged with the settings passed to $.ajax).

converters

  • Type: PlainObject
  • Default: {"* text": window.String, "text html": true, "text json": jQuery.parseJSON, "text xml": jQuery.parseXML}

An object containing dataType-to-dataType converters. Each converter’s value is a function that returns the transformed value of the response. (version added: 1.5)

Settings for Ajax Event

beforeSend

  • Type: Function( jqXHR jqXHR, PlainObject settings )

A pre-request callback function that can be used to modify the jqXHR (in jQuery 1.4.x, XMLHTTPRequest) object before it is sent. Use this to set custom headers, etc. The jqXHR and settings objects are passed as arguments. This is an Ajax Event. Returning false in the beforeSend function will cancel the request.

complete

  • Type: Function( jqXHR jqXHR, String textStatus )

A function to be called when the request finishes (after success and error callbacks are executed). The function gets passed two arguments: The jqXHR (in jQuery 1.4.x, XMLHTTPRequest) object and a string categorizing the status of the request ("success", "notmodified", "nocontent", "error", "timeout", "abort", or "parsererror"). As of jQuery 1.5, the complete setting can accept an array of functions. Each function will be called in turn. This is an Ajax Event.

dataFilter

  • Type: Function( String data, String type ) => Anything

A function to be used to handle the raw response data of XMLHttpRequest. This is a pre-filtering function to sanitize the response. You should return the sanitized data. The function accepts two arguments: The raw data returned from the server and the ‘dataType’ parameter.

error

  • Type: Function( jqXHR jqXHR, String textStatus, String errorThrown )

A function to be called if the request fails. The function receives three arguments: The jqXHR (in jQuery 1.4.x, XMLHttpRequest) object, a string describing the type of error that occurred and an optional exception object, if one occurred. Possible values for the second argument (besides null) are “timeout”, “error”, “abort”, and “parsererror”. When an HTTP error occurs, errorThrown receives the textual portion of the HTTP status, such as “Not Found” or “Internal Server Error.” (in HTTP/2 it may instead be an empty string) As of jQuery 1.5, the error setting can accept an array of functions. Each function will be called in turn. Note: This handler is not called for cross-domain script and cross-domain JSONP requests. This is an Ajax Event.

statusCode

  • Type: PlainObject
  • Default: {}

An object of numeric HTTP codes and functions to be called when the response has the corresponding code. For example, the following will alert when the response status is a 404:

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$.ajax({
statusCode: {
404: function() {
alert( "page not found" );
}
}
});

success

  • Type: Function( Anything data, String textStatus, jqXHR jqXHR )

A function to be called if the request succeeds. The function gets passed three arguments: The data returned from the server, formatted according to the dataType parameter or the dataFilter callback function, if specified; a string describing the status; and the jqXHR (in jQuery 1.4.x, XMLHttpRequest) object.

Settings for Global Ajax Event

global

  • Type: Boolean
  • default: true

Whether to trigger global Ajax event handlers for this request. The default is true. Set to false to prevent the global handlers like ajaxStart or ajaxStop from being triggered.

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.

overrideMimeType()

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:

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$.ajax({
url: "https://fiddle.jshell.net/favicon.png",
beforeSend: function( xhr ) {
xhr.overrideMimeType( "text/plain; charset=x-user-defined" );
}
})
.done(function( data ) {
if ( console && console.log ) {
console.log( "Sample of data:", data.slice( 0, 100 ) );
}
});

Promise interface

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, 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 ) { }); (added in jQuery 1.6)

    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 removed as of jQuery 3.0. You can use jqXHR.done(), jqXHR.fail(), and jqXHR.always() instead.

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// 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" );
});

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
  • responseXML and/or responseText when the underlying request responded with xml and/or text, respectively
  • status
  • statusText (may be an empty string in HTTP/2)
  • abort( [ statusText ] )
  • getAllResponseHeaders() as a string
  • getResponseHeader( name )
  • overrideMimeType( mimeType )
  • 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
  • statusCode( callbacksByStatusCode )

No onreadystatechange mechanism is provided, however, since done, fail, always, and statusCode cover all conceivable requirements.

Data Type

Different types of response to $.ajax() call are subjected to different kinds of pre-processing before being passed to the success handler. The type of pre-processing depends by default upon the Content-Type of the response, but can be set explicitly using the dataType option. If the dataType option is provided, the Content-Type header of the response will be disregarded.

The available data types are text, html, xml, json, jsonp, and script.

If text or html is specified, no pre-processing occurs. The data is simply passed on to the success handler, and made available through the responseText property of the jqXHR object.

If xml is specified, the response is parsed using jQuery.parseXML before being passed, as an XMLDocument, to the success handler. The XML document is made available through the responseXML property of the jqXHR object.

If json is specified, the response is parsed using jQuery.parseJSON before being passed, as an object, to the success handler. The parsed JSON object is made available through the responseJSON property of the jqXHR object.

If script is specified, $.ajax() will execute the JavaScript that is received from the server before passing it on to the success handler as a string.

If jsonp is specified, $.ajax() will automatically append a query string parameter of (by default) callback=? to the URL. The jsonp and jsonpCallback properties of the settings passed to $.ajax() can be used to specify, respectively, the name of the query string parameter and the name of the JSONP callback function. The server should return valid JavaScript that passes the JSON response into the callback function. $.ajax() will execute the returned JavaScript, calling the JSONP callback function, before passing the JSON object contained in the response to the $.ajax() success handler.

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.

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, port, or protocol.
  • Script and JSONP requests are not subject to the same origin policy restrictions.

Global Ajax Event Handlers

These methods register handlers to be called when certain events, such as initialization or completion, take place for any Ajax request on the page. The global events are fired on each Ajax request if the global property in jQuery.ajaxSetup() is true, which it is by default. Note: Global events are never fired for cross-domain script or JSONP requests, regardless of the value of global.

  • .ajaxStart(), Register a handler to be called when the first Ajax request begins. This is an Ajax Event.
  • .ajaxSend(), Attach a function to be executed before an Ajax request is sent. This is an Ajax Event.
  • .ajaxStop(), Register a handler to be called when all Ajax requests have completed. This is an Ajax Event.
  • .ajaxComplete(), Register a handler to be called when Ajax requests complete. This is an AjaxEvent.
  • .ajaxError(), Register a handler to be called when Ajax requests complete with an error. This is an Ajax Event.
  • .ajaxSuccess(), Attach a function to be executed whenever an Ajax request completes successfully. This is an Ajax Event.

Helper Functions

These functions assist with common idioms encountered when performing Ajax tasks.

  • jQuery.param(), Create a serialized representation of an array, a plain object, or a jQuery object suitable for use in a URL query string or Ajax request. In case a jQuery object is passed, it should contain input elements with name/value properties.
  • .serialize(), Encode a set of form elements as a string for submission.
  • .serializeArray(), Encode a set of form elements as an array of names and values.

Low-Level Interface

These methods can be used to make arbitrary Ajax requests.

jQuery.ajax()

Perform an asynchronous HTTP (Ajax) request.

jQuery.ajaxPrefilter()

Handle custom Ajax options or modify existing options before each request is sent and before they are processed by $.ajax().

jQuery.ajaxSetup()

Set default values for future Ajax requests. Its use is not recommended.

jQuery.ajaxTransport()

Creates an object that handles the actual transmission of Ajax data.

Shorthand Methods

These methods perform the more common types of Ajax requests in less code.

jQuery.get()

Load data from the server using a HTTP GET request.

jQuery.getJSON()

Load JSON-encoded data from the server using a GET HTTP request.

jQuery.getScript()

Load a JavaScript file from the server using a GET HTTP request, then execute it.

jQuery.post()

Send data to the server using a HTTP POST request.

.load()

Load data from the server and place the returned HTML into the matched elements.

Summary

Ajax request with query string:

  • traditional: true
  • processData: true
  • data: {JSON object}

Ajax request with application/json

  • contentType: ‘application/json’
  • processData: false
  • traditional: false
  • data: “{JSON string}”

Ajax request with application/x-www-form-urlencoded

  • type: ‘POST’
  • contentType: ‘application/x-www-form-urlencoded’
  • processData: false
  • traditional: false
  • data: form.serialize()

Ajax request with multipart/form-data

  • type: ‘POST’
  • contentType: ‘multipart/form-data’
  • processData: false
  • traditional: false
  • data: formdata

References

[1] jQuery API Documentation

Contents
  1. 1. jQuery Ajax Basic
    1. 1.1. Ajax Requests
    2. 1.2. Ajax Settings
      1. 1.2.1. Settings for Request
      2. 1.2.2. Settings for Response
      3. 1.2.3. Settings for Ajax Event
      4. 1.2.4. Settings for Global Ajax Event
    3. 1.3. The jqXHR Object
      1. 1.3.1. overrideMimeType()
      2. 1.3.2. Promise interface
    4. 1.4. Data Type
    5. 1.5. Sending Data to the Server
    6. 1.6. Additional Notes
  2. 2. Global Ajax Event Handlers
  3. 3. Helper Functions
  4. 4. Low-Level Interface
  5. 5. Shorthand Methods
  6. 6. Summary
  7. 7. References