jQuery $.ajax()

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jQuery.ajax()

jQuery.ajax( url [, settings ] )Returns:jqXHR

Description: Perform an asynchronous HTTP (Ajax) request.

  • version added:1.5jQuery.ajax( url [, settings ] )

    • url
      Type: String
      A string containing the URL to which the request is sent.
    • settings
      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(). SeejQuery.ajax( settings ) below for a complete list of all settings.
    • //解释一下：URL为必要选项，settings是对ajax的一些配置，都是可选的。

  • version added:1.0jQuery.ajax( [settings ] )

    • settings
      A set of key/value pairs that configure the Ajax request. All settings are optional. A default can be set for any option with$.ajaxSetup().
    • //解释一下：全部设置均是以键值对的形式进行设置的，并且都是可选的。
      • accepts (default: depends on DataType)
        The content type sent in the request header that tells the server what kind of response it will accept in return.
      • //解释一下：accepts在请求头里面设置响应的数据返回类型（默认是dataType里面设置的值）。
      • async (default: true)
        By default, all requests are sent asynchronously (i.e. this is set totrue by default). If you need synchronous requests, set this option tofalse. Cross-domain requests and dataType: "jsonp" requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active.As of jQuery 1.8, the use of async: false with jqXHR ($.Deferred) is deprecated; you must use the success/error/complete callback options instead of the corresponding methods of the jqXHR object such asjqXHR.done() or the deprecated jqXHR.success().
      • //解释一下：async是指处理请求时是否是异步处理（布尔类型），设置TRUE表示异步处理（默认值为TRUE）。

        当你须要同步请求时，设置为FALSE。

        跨域和dataType为jsonp的情况不支持同步这个选项。

        须要注意的是设置为同步可能会锁住浏览器，让其它请求不可用。

        所以一般设置为TRUE。


      • 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. Returningfalse 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.
      • //解释一下：beforeSend设置发送请求前的动作。


      • cache (default: true, false for dataType ‘script‘ and ‘jsonp‘)
        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.
      • //解释一下：cache缓存，默认是TRUE（有缓存的）。

        假设设置为FALSE，则不会缓存。

        注意，仅仅有在请求方式为head和get时，才干设置不缓存。

      • complete
        Type: Function( jqXHR jqXHR,String textStatus )
        A function to be called when the request finishes (aftersuccess 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", "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 anAjax Event.
      • //解释一下：complete请求完毕时（不管成功与否）运行的回调函数，有两个參数jqXHR和textStatus。textStatus有下面几种状态：success（成功）、notmodified（没有改动）、error（错误）、timeout（请求超时）、abort（请求被废弃）、parseerror（请求时转换错误）。
      • contents
      • An object of string/regular-expression pairs that determine how jQuery will parse the response, given its content type. (version added:1.5)
      • //解释一下：contents设置正則表達式来决定jQuery怎么来转换响应。
      • contentType (default: ‘application/x-www-form-urlencoded; charset=UTF-8‘)
        Type: 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). 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 thanapplication/x-www-form-urlencoded, multipart/form-data, ortext/plain will trigger the browser to send a preflight OPTIONS request to the server.
      • //解释一下：contentType编码设置，默认是‘application/x-www-form-urlencoded; charset=UTF-8‘。utf-8编码，国际通用编码。默认即可了，适用绝大多数情况。


      • context
        This object will be made 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 thecomplete callback of a request, like so:
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        $.ajax({
          url: "test.html",
          context: document.body
        }).done(function() {
          $( this ).addClass( "done" );

        });
      • //解释一下：context上下文。通常能够定义一个变量来存放上下文。


      • converters (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
      • //解释一下：converters转换器，默认值是{"* text": window.String, "text html": true, "text json": jQuery.parseJSON, "text xml": jQuery.parseXML}。
      • crossDomain (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 totrue. This allows, for example, server-side redirection to another domain. (version added:1.5)
      • //解释一下：crossDomain跨域。默认值是FALSE。


      • data
        Data to be sent to the server. It is converted to a query string, if not already a string. It‘s appended to the url for GET-requests. SeeprocessData option to prevent this automatic processing. Object must be Key/Value pairs. If value is an Array, jQuery serializes multiple values with same key based on the value of thetraditional setting (described below).
      • //解释一下：data以键值对的形式向server发送数据，通常能够将表单里面的数据传递$("#form").serialize()。
      • 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.
      • //解释一下：dataFilter数据过滤器。
      • dataType (default: Intelligent Guess (xml, json, script, or html))
        Type: String
        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 (an XML MIME type will yield XML, in 1.4 JSON will yield a javascript object, in 1.4 script will execute the script, and anything else will be returned as a string). The available types (and the result passed as the first argument to your success callback) are:
        • "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 thecache 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. (Seejson.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 thecache 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.
        • //解释一下：dataType返回的数据类型，通常有XML、json、script、text和HTML等。假设不设置，jQuery会依据响应的MIME类型设置。用的最多的是json、XML和text。
      • 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 anAjax Event.
      • //解释一下：error请求失败时调用的函数。有三个參数 jqXHR、textStatus、errorThrown。

        textStatus可能的值：timeout、error、abort和parseerror。

      • global (default: true)
        Whether to trigger global Ajax event handlers for this request. The default istrue. Set to false to prevent the global handlers like ajaxStart or ajaxStop from being triggered. This can be used to control variousAjax Events.
      • //解释一下：global请求时是否触发全局的ajax事件，默认是TRUE。
      • headers (default: {})
        An object of additional header key/value pairs to send along with requests using the XMLHttpRequest transport. The headerX-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 thebeforeSend function. (version added: 1.5)
      • //解释一下：headers键值对的形式。
      • ifModified (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 isfalse, ignoring the header. In jQuery 1.4 this technique also checks the ‘etag‘ specified by the server to catch unmodified data.
      • //解释一下：ifModified默认是FALSE，忽略header。
      • isLocal (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)
      • //解释一下：isLocal默认依赖于当前的协议。
      • 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 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 thejsonpCallback setting. For example, { jsonp: false, jsonpCallback: "callbackName" }

      • //解释一下：jsonp查询时设置URL用的，假设设置jsonp：‘onJsonpLoad’就会向server传送onJSONPLoad=?。在jQuery1.5后，设置{ jsonp: false, jsonpCallback: "callbackName" }。
      • jsonpCallback
        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 function for this setting, in which case the value ofjsonpCallback is set to the return value of that function.
      • //解释一下：jsonpCallback。JOSNP请求的回调函数。
      • mimeType
        Type: String
        A mime type to override the XHR mime type. (version added: 1.5.1)
      • //解释一下：mimeType设置MIME类型。
      • password
        Type: String
        A password to be used with XMLHttpRequest in response to an HTTP access authentication request.
      • //解释一下：password在XMLHttpRequest响应时加密的密码。


      • processData (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 tofalse.
      • //解释一下：processData默认TRUE。针对contentType为 "application/x-www-form-urlencoded"。
      • scriptCharset
        Type: String
        Only applies when the "script" transport is used (e.g., cross-domain requests with "jsonp" or "script" dataType and "GET" type). Sets thecharset 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.
      • //解释一下：scriptCharset脚本编码。


      • statusCode (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" );
            }
          }
        });

        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 theerror callback.

        (version added: 1.5)
      • //解释一下：statusCode状态码，常见的有404、500等。详细參考百度。
      • 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 thedataType parameter or the dataFilter callback function, if specified; a string describing the status; and thejqXHR (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 anAjax Event.
      • //解释一下：success请求成功时被调用的函数，有三个參数data、textStatus和jqXHR。


      • 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.
      • //解释一下：timeout设置请求的超时时间。
      • traditional
        Set this to true if you wish to use the traditional style ofparam serialization.
      • //解释一下：traditional，设置TRUE使用传统的參数序列化。
      • type (default: ‘GET‘)
        Type: String
        The type of request to make ("POST" or "GET"), default is "GET".Note: Other HTTP request methods, such as PUT and DELETE, can also be used here, but they are not supported by all browsers.
      • //解释一下：type请求的方式通常有post和get，默觉得get。put和delete部分浏览器支持。
      • url (default: The current page)
        Type: String
        A string containing the URL to which the request is sent.
      • //解释一下：URL请求处理路径。


      • username
        Type: String
        A username to be used with XMLHttpRequest in response to an HTTP access authentication request.
      • //解释一下：username。HTTP认证时的用户名。


      • 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.
      • //解释一下：xhr默认ActiveXObject（IE浏览器） or XMLHttpRequest（其余浏览器）。
      • xhrFields

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

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

        In jQuery 1.5, the withCredentials property was not propagated to the nativeXHR 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:

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$.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 containsresponseText 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) thejqXHR object simulates native XHR functionality where possible.

As of jQuery 1.5.1, the jqXHR object also contains theoverrideMimeType() 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: "http://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 ) );
    }
  });

The jqXHR objects returned by $.ajax() as of jQuery 1.5 implement the Promise interface, giving them all the properties, methods, and behavior of a Promise (seeDeferred object for more information). These methods take one or more function arguments that are called when the$.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 todeferred.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 todeferred.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 todeferred.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, usejqXHR.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" );
});

//解释一下：done、fail和always分别取代success、error和complete。前者是官方推荐。


The this reference within all callbacks is the object in thecontext 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, ajqXHR 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, sincedone, 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 anddone, 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. SeeDeferred object methods, which are implemented internally for these$.ajax() callback hooks.

The callback hooks provided by $.ajax() are as follows:

  1. beforeSend callback option is invoked; it receives thejqXHR object and the settings object as parameters.
  2. error callback option is invoked, if the request fails. It receives 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".
  3. dataFilter callback option 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 to success.
  4. success callback option is invoked, if the request succeeds. It receives the returned data, a string containing the success code, and thejqXHR object.
  5. Promise callbacks — .done(),.fail(), .always(), and .then() — are invoked, in the order they are registered.
  6. complete callback option fires, when the request finishes, whether in failure or success. It receives thejqXHR object, as well as a string containing the success or error code.

Data Types

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 thedataType 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 theresponseText property of the jqXHR object.

//解释一下：dataType是简单的字符串。


If xml is specified, the response is parsed usingjQuery.parseXML before being passed, as anXMLDocument, to the success handler. The XML document is made available through theresponseXML property of the jqXHR object.

//解释一下：dataType为XML，用jquery.parseXML转换为一个XML树。

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

//解释一下：dataType为json，用jquery.parseJSON处理。


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.

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 thetype 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 formkey1=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 usingjQuery.param() before it is sent. This processing can be circumvented by settingprocessData to false. The processing might be undesirable if you wish to send an XML object to the server; in this case, change thecontentType 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 tofalse. 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 theusername 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 thetimeout option.

By default, requests are always issued, but the browser may serve results out of its cache. To disallow use of the cached results, setcache to false. To cause the request to report failure if the asset has not been modified since the last request, setifModified 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. Theasync option to $.ajax() defaults to true, indicating that code execution can continue after the request is made. Setting this option tofalse (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 thexhr 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 includesprefilters,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.gjson), you must add a correspondance between the response Content-Type and the actual data type using thecontents option:

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$.ajaxSetup({
  contents: {
    mycustomtype: /mycustomtype/
  },
  converters: {
    "mycustomtype json": function( result ) {
      // Do stuff
      return newresult;
    }
  }
});

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:

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$.ajaxSetup({
  contents: {
    mycustomtype: /mycustomtype/
  },
  converters: {
    "text mycustomtype": true,
    "mycustomtype json": function( result ) {
      // Do stuff
      return newresult;
    }
  }
});

The above now allows passing from text tomycustomtype and then mycustomtype to json.

Additional Notes:

  • Due to browser security restrictions, most "Ajax" requests are subject to thesame 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.

Examples:

Example: Save some data to the server and notify the user once it‘s complete.

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$.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.

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$.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 tofalse, the automatic conversion of data to strings is prevented.

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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",
  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.

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$.ajax({
  type: "GET",
  url: "test.js",
  dataType: "script"
});






































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