Given a jQuery object that represents a set of DOM elements, the .add() method constructs a new jQuery object from the union of those elements and the ones passed into the method. The argument to .add() can be pretty much anything that $() accepts, including a jQuery selector expression, references to DOM elements, or an HTML snippet.

Do not assume that this method appends the elements to the existing collection in the order they are passed to the .add() method. When all elements are members of the same document, the resulting collection from .add() will be sorted in document order; that is, in order of each element's appearance in the document. If the collection consists of elements from different documents or ones not in any document, the sort order is undefined. To create a jQuery object with elements in a well-defined order and without sorting overhead, use the $(array_of_DOM_elements) signature.

The updated set of elements can be used in a following (chained) method, or assigned to a variable for later use. For example:

$( "p" ).add( "div" ).addClass( "widget" );
var pdiv = $( "p" ).add( "div" );

The following will not save the added elements, because the .add() method creates a new set and leaves the original set in pdiv unchanged:

var pdiv = $( "p" );
pdiv.add( "div" ); // WRONG, pdiv will not change

Consider a page with a simple list and a paragraph following it:

<ul>
  <li>list item 1</li>
  <li>list item 2</li>
  <li>list item 3</li>
</ul>
<p>a paragraph</p>

We can select the list items and then the paragraph by using either a selector or a reference to the DOM element itself as the .add() method's argument:

$( "li" ).add( "p" ).css( "background-color", "red" );

Or:

$( "li" ).add( document.getElementsByTagName( "p" )[ 0 ] )
  .css( "background-color", "red" );

The result of this call is a red background behind all four elements. Using an HTML snippet as the .add() method's argument (as in the third version), we can create additional elements on the fly and add those elements to the matched set of elements. Let's say, for example, that we want to alter the background of the list items along with a newly created paragraph:

$( "li" ).add( "<p id='new'>new paragraph</p>" )
  .css( "background-color", "red" );

Although the new paragraph has been created and its background color changed, it still does not appear on the page. To place it on the page, we could add one of the insertion methods to the chain.

As of jQuery 1.4 the results from .add() will always be returned in document order (rather than a simple concatenation).

Note: To reverse the .add() you can use .not( elements | selector ) to remove elements from the jQuery results, or .end() to return to the selection before you added.

As described in the discussion for .end(), jQuery objects maintain an internal stack that keeps track of changes to the matched set of elements. When one of the DOM traversal methods is called, the new set of elements is pushed onto the stack. If the previous set of elements is desired as well, .addBack() can help.

Consider a page with a simple list on it:

<ul>
  <li>list item 1</li>
  <li>list item 2</li>
  <li class="third-item">list item 3</li>
  <li>list item 4</li>
  <li>list item 5</li>
</ul>

The result of the following code is a red background behind items 3, 4 and 5:

$( "li.third-item" ).nextAll().addBack()
  .css( "background-color", "red" );

First, the initial selector locates item 3, initializing the stack with the set containing just this item. The call to .nextAll() then pushes the set of items 4 and 5 onto the stack. Finally, the .addBack() invocation merges these two sets together, creating a jQuery object that points to all three items in document order: {[<li.third-item>,<li>,<li> ]}.

It's important to note that this method does not replace a class. It simply adds the class, appending it to any which may already be assigned to the elements.

Before jQuery version 1.12/2.2, the .addClass() method manipulated the className property of the selected elements, not the class attribute. Once the property was changed, it was the browser that updated the attribute accordingly. An implication of this behavior was that this method only worked for documents with HTML DOM semantics (e.g., not pure XML documents).

As of jQuery 1.12/2.2, this behavior is changed to improve the support for XML documents, including SVG. Starting from this version, the class attribute is used instead. So, .addClass() can be used on XML or SVG documents.

More than one class may be added at a time, separated by a space, to the set of matched elements, like so:

$( "p" ).addClass( "myClass yourClass" );

This method is often used with .removeClass() to switch elements' classes from one to another, like so:

$( "p" ).removeClass( "myClass noClass" ).addClass( "yourClass" );

Here, the myClass and noClass classes are removed from all paragraphs, while yourClass is added.

As of jQuery 1.4, the .addClass() method's argument can receive a function.

$( "ul li" ).addClass(function( index ) {
  return "item-" + index;
});

Given an unordered list with two <li> elements, this example adds the class "item-0" to the first <li> and "item-1" to the second.

The .after() and .insertAfter() methods perform the same task. The major difference is in the syntax—specifically, in the placement of the content and target. With .after(), the content to be inserted comes from the method's argument: $(target).after(contentToBeInserted). With .insertAfter(), on the other hand, the content precedes the method and is inserted after the target, which in turn is passed as the .insertAfter() method's argument: $(contentToBeInserted).insertAfter(target).

Using the following HTML:

<div class="container">
  <h2>Greetings</h2>
  <div class="inner">Hello</div>
  <div class="inner">Goodbye</div>
</div>

Content can be created and then inserted after several elements at once:

$( ".inner" ).after( "<p>Test</p>" );

Each inner <div> element gets this new content:

<div class="container">
  <h2>Greetings</h2>
  <div class="inner">Hello</div>
  <p>Test</p>
  <div class="inner">Goodbye</div>
  <p>Test</p>
</div>

An element in the DOM can also be selected and inserted after another element:

$( ".container" ).after( $( "h2" ) );

If an element selected this way is inserted into a single location elsewhere in the DOM, it will be moved rather than cloned:

<div class="container">
  <div class="inner">Hello</div>
  <div class="inner">Goodbye</div>
</div>
<h2>Greetings</h2>

Important: If there is more than one target element, however, cloned copies of the inserted element will be created for each target except for the last one.

Passing a Function

As of jQuery 1.4, .after() supports passing a function that returns the elements to insert.

$( "p" ).after(function() {
  return "<div>" + this.className + "</div>";
});

This example inserts a <div> after each paragraph, with each new <div> containing the class name(s) of its preceding paragraph.

Additional Arguments

Similar to other content-adding methods such as .prepend() and .before(), .after() also supports passing in multiple arguments as input. Supported input includes DOM elements, jQuery objects, HTML strings, and arrays of DOM elements.

For example, the following will insert two new <div>s and an existing <div> after the first paragraph:

var $newdiv1 = $( "<div id='object1'></div>" ),
  newdiv2 = document.createElement( "div" ),
  existingdiv1 = document.getElementById( "foo" );
 
$( "p" ).first().after( $newdiv1, [ newdiv2, existingdiv1 ] );

Since .after() can accept any number of additional arguments, the same result can be achieved by passing in the three <div>s as three separate arguments, like so: $( "p" ).first().after( $newdiv1, newdiv2, existingdiv1 ). The type and number of arguments will largely depend on the elements that are collected in the code.

• Prior to jQuery 1.9, .after() would attempt to add or change nodes in the current jQuery set if the first node in the set was not connected to a document, and in those cases return a new jQuery set rather than the original set. The method might or might not have returned a new result depending on the number or connectedness of its arguments! As of jQuery 1.9, .after(), .before(), and .replaceWith() always return the original unmodified set. Attempting to use these methods on a node without a parent has no effect—that is, neither the set nor the nodes it contains are changed.
• By design, any jQuery constructor or method that accepts an HTML string — jQuery(), .append(), .after(), etc. — can potentially execute code. This can occur by injection of script tags or use of HTML attributes that execute code (for example, <img onload="">). Do not use these methods to insert strings obtained from untrusted sources such as URL query parameters, cookies, or form inputs. Doing so can introduce cross-site-scripting (XSS) vulnerabilities. Remove or escape any user input before adding content to the document.

Whenever an Ajax request completes, jQuery triggers the ajaxComplete event. Any and all registered ajaxComplete handlers are executed at this time.

To observe this method in action, set up a basic Ajax load request:

<div class="trigger">Trigger</div>
<div class="result"></div>
<div class="log"></div>

Attach the event handler to the document:

$( document ).on( "ajaxComplete", function() {
  $( ".log" ).text( "Triggered ajaxComplete handler." );
} );

Now, make an Ajax request using any jQuery method:

$( ".trigger" ).on( "click", function() {
  $( ".result" ).load( "ajax/test.html" );
} );

When the user clicks the element with class trigger and the Ajax request completes, the log message is displayed.

All ajaxComplete handlers are invoked, regardless of what Ajax request was completed. If you must differentiate between the requests, use the parameters passed to the handler. Each time an ajaxComplete handler is executed, it is passed the event object, the XMLHttpRequest object, and the settings object that was used in the creation of the request. For example, you can restrict the callback to only handling events dealing with a particular URL:

$( document ).on( "ajaxComplete", function( event, xhr, settings ) {
  if ( settings.url === "ajax/test.html" ) {
    $( ".log" ).text( "Triggered ajaxComplete handler. The result is " +
      xhr.responseText );
  }
} );

Note: You can get the returned Ajax contents by looking at xhr.responseText.

• As of jQuery 1.9, all the handlers for the jQuery global Ajax events, including those added with .on( "ajaxComplete", ... ), must be attached to document.
• If $.ajax() or $.ajaxSetup() is called with the global option set to false, the ajaxComplete event will not fire.

Whenever an Ajax request completes with an error, jQuery triggers the ajaxError event. Any and all registered ajaxError handlers are executed at this time. Note: This handler is not called for cross-domain script and cross-domain JSONP requests.

To observe this method in action, set up a basic Ajax load request.

<button class="trigger">Trigger</button>
<div class="result"></div>
<div class="log"></div>

Attach the event handler to the document:

$( document ).on( "ajaxError", function() {
  $( ".log" ).text( "Triggered ajaxError handler." );
} );

Now, make an Ajax request using any jQuery method:

$( "button.trigger" ).on( "click", function() {
  $( "div.result" ).load( "ajax/missing.html" );
} );

When the user clicks the button and the Ajax request fails, because the requested file is missing, the log message is displayed.

All ajaxError handlers are invoked, regardless of what Ajax request was completed. To differentiate between the requests, use the parameters passed to the handler. Each time an ajaxError handler is executed, it is passed the event object, the jqXHR object (prior to jQuery 1.5, the XHR object), and the settings object that was used in the creation of the request. When an HTTP error occurs, the fourth argument (thrownError) receives the textual portion of the HTTP status, such as "Not Found" or "Internal Server Error." For example, to restrict the error callback to only handling events dealing with a particular URL:

$( document ).on( "ajaxError", function( event, jqxhr, settings, thrownError ) {
  if ( settings.url == "ajax/missing.html" ) {
    $( "div.log" ).text( "Triggered ajaxError handler." );
  }
} );

• As of jQuery 1.9, all the handlers for the jQuery global Ajax events, including those added with .on( "ajaxError", ... ), must be attached to document.
• If $.ajax() or $.ajaxSetup() is called with the global option set to false, the ajaxError event will not fire.

Whenever an Ajax request is about to be sent, jQuery triggers the ajaxSend event. Any and all registerd ajaxSend handlers are executed at this time.

To observe this method in action, set up a basic Ajax load request:

<div class="trigger">Trigger</div>
<div class="result"></div>
<div class="log"></div>

Attach the event handler to the document:

$( document ).on( "ajaxSend", function() {
  $( ".log" ).text( "Triggered ajaxSend handler." );
} );

Now, make an Ajax request using any jQuery method:

$( ".trigger" ).on( "click", function() {
  $( ".result" ).load( "ajax/test.html" );
} );

When the user clicks the element with class trigger and the Ajax request is about to begin, the log message is displayed.

All ajaxSend handlers are invoked, regardless of what Ajax request is to be sent. If you must differentiate between the requests, use the parameters passed to the handler. Each time an ajaxSend handler is executed, it is passed the event object, the jqXHR object (in version 1.4, XMLHttpRequestobject), and the settings object that was used in the creation of the Ajax request. For example, you can restrict the callback to only handling events dealing with a particular URL:

$( document ).on( "ajaxSend", function( event, jqxhr, settings ) {
  if ( settings.url == "ajax/test.html" ) {
    $( ".log" ).text( "Triggered ajaxSend handler." );
  }
} );

• As of jQuery 1.9, all the handlers for the jQuery global Ajax events, including those added with .on( "ajaxSend", ... ), must be attached to document.
• If $.ajax() or $.ajaxSetup() is called with the global option set to false, the ajaxSend event will not fire.