jQuery.ajax()
Description: Perform an asynchronous HTTP (Ajax) request.
jQuery.ajax( settings )
settings
A set of key/value pairs that configure the Ajax request. All options are optional. A default can be set for any option with $.ajaxSetup().
The
At its simplest, 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, $.ajax() can be used more flexibly.$.ajax() function can be called with no arguments:$.ajax();
Note: Default settings can be set globally by using the
$.ajaxSetup() function.This example, using no options, loads the contents of the current page, but does nothing with the result. To use the result, we can implement one of the callback functions.
Callback Functions
The
beforeSend, error, dataFilter, success and complete options all take callback functions that are invoked at the appropriate times:beforeSendis called before the request is sent, and is passed theXMLHttpRequestobject as a parameter.erroris called if the request fails. It is passed theXMLHttpRequestobject, a string indicating the error type, and an exception object if applicable.dataFilteris called on success. It is passed the returned data and the value ofdataType, and must return the (possibly altered) data to pass on tosuccess.successis called if the request succeeds. It is passed the returned data, as well as a string containing the success code.completeis called when the request finishes, whether in failure or success. It is passed theXMLHttpRequestobject, as well as a string containing the success or error code.
To make use of the returned HTML, we can implement a
success handler:$.ajax({
url: 'ajax/test.html',
success: function(data) {
$('.result').html(data);
alert('Load was performed.');
}
});Such a simple example would generally be better served by using
.load() or $.get().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 responseHTML property of the XMLHttpRequest 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 the script itself as textual data.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 JSON.parse() when the browser supports it; otherwise it uses a Function constructor. 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, the jsonp type can be used instead. This type will cause a query string parameter of callback=? to be appended to the URL; the server should prepend the JSON data with the callback name to form a valid JSONP response. If a specific parameter name is desired instead of callback, it can be specified 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 operation is performed using a <script> tag rather than an XMLHttpRequest object. In this case, no XMLHttpRequest object is returned from $.ajax(), nor is one passed to the handler functions such as beforeSend.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.The
data option can contain either a query string of the form key1=value1&key2=value2, or a map of the form {key1: 'value1', key2: 'value2'}. If the latter form is used, the data is converted into a query string before it is sent. This processing can be circumvented by setting processData to false. The processing might be undesirable if we wish to send an XML object to the server; in this case, we would also want to 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. 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.Examples:
Example: Load and execute a JavaScript file.
$.ajax({
type: "GET",
url: "test.js",
dataType: "script"
});Example: Save some data to the server and notify the user once it's complete.
$.ajax({
type: "POST",
url: "some.php",
data: "name=John&location=Boston",
success: function(msg){
alert( "Data Saved: " + msg );
}
});Example: Retrieve the latest version of an HTML page.
$.ajax({
url: "test.html",
cache: false,
success: function(html){
$("#results").append(html);
}
});Example: Loads data synchronously. Blocks the browser while the requests is active. It is better to block user interaction by other means when synchronization is necessary.
var html = $.ajax({
url: "some.php",
async: false
}).responseText;Example: Sends an xml document as data to the server. By setting the processData option to false, the automatic conversion of data to strings is prevented.
var xmlDocument = [create xml document];
$.ajax({
url: "page.php",
processData: false,
data: xmlDocument,
success: handleResponse
});Example: Sends an id as data to the server, save some data to the server and notify the user once it's complete.
bodyContent = $.ajax({
url: "script.php",
global: false,
type: "POST",
data: ({id : this.getAttribute('id')}),
dataType: "html",
success: function(msg){
alert(msg);
}
}
).responseText;Tags: jQuery, library
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