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jQuery.ajax()
Categories: Ajax > Low-Level Interface
jQuery.ajax( url [, settings ] )Returns: jqXHR Description: Perform an asynchronous HTTP (Ajax) request.
- version added: 1.5 jQuery.ajax( url [, settings ] )
- url Type: String A string containing the URL to which the request is sent.
- 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(). See jQuery.ajax( settings ) below for a complete list of all settings.
- version added: 1.0 jQuery.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(). ■ accepts (default: depends on DataType) Type: PlainObject The content type sent in the request header that tells the server what kind of response it will accept in return. ■ async (default: true) Type: Boolean 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. As of jQuery 1.8, the use of async: false with jqXHR ( $.Deferred) is deprecated; you must use the success/error/complete callback options instead of the corresponding methods of the jqXHR object such as jqXHR.done() or the deprecated jqXHR.success(). ■ 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. As of jQuery 1.5 , the beforeSend option will be called regardless of the type of request. ■ cache (default: true, false for dataType 'script' and 'jsonp' ) Type: Boolean If set to false, it will force requested pages not to be cached by the browser. Note: Setting cache to false will only work correctly with HEAD and GET requests. It works by appending "_={timestamp}" to the GET parameters. The parameter is not needed for other types of requests, except in IE8 when a POST is made to a URL that has already been requested by a GET. ■ 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. ■ 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) ■ contentType (default: 'application/x-www-form-urlencoded; charset=UTF-8') Type: Boolean or String 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 $.ajax(), then it is always sent to the server (even if no data is sent). As of jQuery 1.6 you can pass false to tell jQuery to not set any content type header. Note: The W3C XMLHttpRequest specification dictates that the charset is always UTF-8; specifying another charset will not force the browser to change the encoding. Note: For cross-domain requests, setting the content type to anything other than application/x-www-form-urlencoded , multipart/form-data, or text/plain will trigger the browser to send a preflight OPTIONS request to the server. ■ context Type: PlainObject This object will be the context of all Ajax-related callbacks. By default, the context is an object that represents the Ajax settings used in the call ($.ajaxSettings merged with the settings passed to $.ajax). For example, specifying a DOM element as the context will make that the context for the complete callback of a request, like so:
1 $.ajax({
■ "xml": Returns a XML document that can be processed via jQuery. ■ (^) "html": Returns HTML as plain text; included script tags are evaluated when inserted in the DOM. ■ "script": Evaluates the response as JavaScript and returns it as plain text. Disables caching by appending a query string parameter, "=[TIMESTAMP]", to the URL unless the cache option is set to true. Note: This will turn POSTs into GETs for remote-domain requests. ■ "json": Evaluates the response as JSON and returns a JavaScript object. The JSON data is parsed in a strict manner; any malformed JSON is rejected and a parse error is thrown. As of jQuery 1.9, an empty response is also rejected; the server should return a response of null or {} instead. (See json.org for more information on proper JSON formatting.) ■ "jsonp": Loads in a JSON block using JSONP. Adds an extra "?callback=?" to the end of your URL to specify the callback. Disables caching by appending a query string parameter, "= [TIMESTAMP]", to the URL unless the cache option is set to true. ■ "text": A plain text string. ■ 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. You can also make a JSONP request, have it received as text, and interpreted by jQuery as XML: "jsonp text xml." Similarly, a shorthand string such as "jsonp xml" will first attempt to convert from jsonp to xml, and, failing that, convert from jsonp to text, and then from text to xml. ■ 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." 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.
■ global (default: true) Type: Boolean 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. This can be used to control various Ajax Events. ■ headers (default: {}) Type: PlainObject 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 (default: false) Type: Boolean 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 (default: depends on current location protocol ) Type: Boolean 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 $.ajaxSetup() method. (version added: 1.5.1) ■ jsonp Type: String Override the callback function name in a JSONP request. This value will be used instead of 'callback' in the 'callback=?' part of the query string in the url. So {jsonp:'onJSONPLoad'} would result in 'onJSONPLoad=?' passed to the server. As of jQuery 1.5 , setting the jsonp option to falseprevents jQuery from adding the "? callback" string to the URL or attempting to use "=?" for transformation. In this case, you should also explicitly set the jsonpCallback setting. For example, { jsonp: false, jsonpCallback: "callbackName" } ■ jsonpCallback Type: String or Function() Specify the callback function name for a JSONP request. This value will be used instead of the random name automatically generated by jQuery. It is preferable to let jQuery generate a unique name as it'll make it easier to manage the requests and provide callbacks and error handling. You may want to specify the callback when you want to enable better browser caching of GET requests. As of jQuery 1.5 , you can also use a
If the request is successful, the status code functions take the same parameters as the success callback; if it results in an error (including 3xx redirect), they take the same parameters as the errorcallback.
(version added: 1.5) ■ success Type: Function( Anything data, String textStatus, jqXHR jqXHR ) A function to be called if the request succeeds. The function gets passed three arguments: The data returned from the server, formatted according to the dataType parameter or the dataFiltercallback function, if specified; a string describing the status; and the jqXHR (in jQuery 1.4.x, XMLHttpRequest) object. As of jQuery 1.5 , the success setting can accept an array of functions. Each function will be called in turn. This is an Ajax Event. ■ timeout Type: Number Set a timeout (in milliseconds) for the request. This will override any global timeout set with$.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. In jQuery 1.4.x and below, the XMLHttpRequest object will be in an invalid state if the request times out; accessing any object members may throw an exception. In Firefox 3.0+ only, script and JSONP requests cannot be cancelled by a timeout; the script will run even if it arrives after the timeout period. ■ traditional Type: Boolean Set this to true if you wish to use the traditional style of param serialization. ■ type (default: 'GET') Type: String An alias for method. You should use type if you're using versions of jQuery prior to 1.9.0. ■ url (default: The current page) Type: String 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 (default: ActiveXObject when available (IE), the XMLHttpRequest otherwise) Type: Function()
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.
1 2 3 4 5 6 $.ajax({ url: a_cross_domain_url, xhrFields: { withCredentials: true } });
In jQuery 1.5 , the withCredentials property was not propagated to the native XHR and thus CORS requests requiring it would ignore this flag. For this reason, we recommend using jQuery 1.5.1+ should you require the use of it.
(version added: 1.5.1) 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:
1 $.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, 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
- 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.
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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
- status
- statusText
- responseXML and/or responseText when 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()
- 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:
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.
For more information on JSONP, see the original post detailing its use.
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.
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
$.ajax({ method: "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.
1 2 3 4 5 6 7 $.ajax({ url: "test.html", cache: false }) .done( 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.
1 2 3 4 5 6 7 8 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.
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var menuId = $( "ul.nav" ).first().attr( "id" ); var request = $.ajax({ url: "script.php", method: "POST", data: { id : menuId }, dataType: "html" }); request.done( function ( msg ) { $( "#log" ).html( msg ); }); request.fail( function ( jqXHR, textStatus ) { alert( "Request failed: " + textStatus ); });
Example: Load and execute a JavaScript file.
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$.ajax({ method: "GET", url: "test.js", dataType: "script" });
