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jQuery's Ajax-Related Methods
beginner
jQuery Fundamentals

While jQuery does offer many Ajax-related convenience methods, the core $.ajax method is at the heart of all of them, and understanding it is imperative. We'll review it first, and then touch briefly on the convenience methods.

I generally use the $.ajax method and do not use convenience methods. As you'll see, it offers features that the convenience methods do not, and its syntax is more easily understandable, in my opinion.

$.ajax

jQuery's core $.ajax method is a powerful and straightforward way of creating Ajax requests. It takes a configuration object that contains all the instructions jQuery requires to complete the request. The $.ajax method is particularly valuable because it offers the ability to specify both success and failure callbacks. Also, its ability to take a configuration object that can be defined separately makes it easier to write reusable code. For complete documentation of the configuration options, visit http://api.jquery.com/jQuery.ajax/.

// Using the core $.ajax method
$.ajax({
    // the URL for the request
    url: "post.php",

    // the data to send (will be converted to a query string)
    data: {
        id: 123
    },

    // whether this is a POST or GET request
    type: "GET",

    // the type of data we expect back
    dataType : "json",

    // code to run if the request succeeds;
    // the response is passed to the function
    success: function( json ) {
        $( "<h1/>" ).text( json.title ).appendTo( "body" );
        $( "<div class=\"content\"/>").html( json.html ).appendTo( "body" );
    },

    // code to run if the request fails; the raw request and
    // status codes are passed to the function
    error: function( xhr, status ) {
        alert( "Sorry, there was a problem!" );
    },

    // code to run regardless of success or failure
    complete: function( xhr, status ) {
        alert( "The request is complete!" );
    }
});

Note: A note about the dataType setting: if the server sends back data that is in a different format than you specify, your code may fail, and the reason will not always be clear, because the HTTP response code will not show an error. When working with Ajax requests, make sure your server is sending back the data type you're asking for, and verify that the Content-type header is accurate for the data type. For example, for JSON data, the Content-type header should be application/json.

$.ajax Options

There are many, many options for the $.ajax method, which is part of its power. For a complete list of options, visit http://api.jquery.com/jQuery.ajax/; here are several that you will use frequently:

async

Set to false if the request should be sent synchronously. Defaults to true. Note that if you set this option to false, your request will block execution of other code until the response is received.

cache

Whether to use a cached response if available. Defaults to true for all dataTypes except "script" and "jsonp". When set to false, the URL will simply have a cachebusting parameter appended to it.

complete

A callback function to run when the request is complete, regardless of success or failure. The function receives the raw request object and the text status of the request.

context

The scope in which the callback function(s) should run (i.e. what this will mean inside the callback function(s)). By default, this inside the callback function(s) refers to the object originally passed to $.ajax.

data

The data to be sent to the server. This can either be an object or a query string, such as foo=bar&amp;baz=bim.

dataType

The type of data you expect back from the server. By default, jQuery will look at the MIME type of the response if no dataType is specified.

error

A callback function to run if the request results in an error. The function receives the raw request object and the text status of the request.

jsonp

The callback name to send in a query string when making a JSONP request. Defaults to "callback".

success

A callback function to run if the request succeeds. The function receives the response data (converted to a JavaScript object if the dataType was JSON), as well as the text status of the request and the raw request object.

timeout

The time in milliseconds to wait before considering the request a failure.

traditional

Set to true to use the param serialization style in use prior to jQuery 1.4. For details, see http://api.jquery.com/jQuery.param/.

type

The type of the request, "POST" or "GET". Defaults to "GET". Other request types, such as "PUT" and "DELETE" can be used, but they may not be supported by all browsers.

url

The URL for the request.

The url option is the only required property of the $.ajax configuration object; all other properties are optional. This can also be passed as the first argument to $.ajax, and the options object as the second argument.

Convenience Methods

If you don't need the extensive configurability of $.ajax, and you don't care about handling errors, the Ajax convenience functions provided by jQuery can be useful, terse ways to accomplish Ajax requests. These methods are just "wrappers" around the core $.ajax method, and simply pre-set some of the options on the $.ajax method.

The convenience methods provided by jQuery are:

$.get

Perform a GET request to the provided URL.

$.post

Perform a POST request to the provided URL.

$.getScript

Add a script to the page.

$.getJSON

Perform a GET request, and expect JSON to be returned.

In each case, the methods take the following arguments, in order:

url

The URL for the request. Required.

data

The data to be sent to the server. Optional. This can either be an object or a query string, such as foo=bar&amp;baz=bim.

Note: This option is not valid for $.getScript.

success callback

A callback function to run if the request succeeds. Optional. The function receives the response data (converted to a JavaScript object if the data type was JSON), as well as the text status of the request and the raw request object.

data type

The type of data you expect back from the server. Optional.

Note: This option is only applicable for methods that don't already specify the data type in their name.

// Using jQuery's Ajax convenience methods

// get plain text or HTML
$.get( "/users.php", {
    userId: 1234
}, function( resp ) {
    console.log( resp ); // server response
});

// add a script to the page, then run a function defined in it
$.getScript( "/static/js/myScript.js", function() {
    functionFromMyScript();
});

// get JSON-formatted data from the server
$.getJSON( "/details.php", function( resp ) {
    // log each key in the response data
    $.each( resp, function( key, value ) {
        console.log( key + " : " + value );
    });
});

$.fn.load

The $.fn.load method is unique among jQuery's Ajax methods in that it is called on a selection. The $.fn.load method fetches HTML from a URL, and uses the returned HTML to populate the selected element(s). In addition to providing a URL to the method, you can optionally provide a selector; jQuery will fetch only the matching content from the returned HTML.

// Using $.fn.load to populate an element
$( "#newContent" ).load( "/foo.html" );
// Using $.fn.load to populate an element based on a selector
$( "#newContent" ).load( "/foo.html #myDiv h1:first:", function( html ) {
    alert( "Content updated!" );
});
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