.delegate()

Categories: Events > Event Handler Attachment | Deprecated > Deprecated 3.0 Chinese Translation: .delegate()

.delegate( selector, eventType, handler )Returns: jQueryversion deprecated: 3.0

Description: Attach a handler to one or more events for all elements that match the selector, now or in the future, based on a specific set of root elements.

  • version added: 1.4.2.delegate( selector, eventType, handler )

    • selector
      Type: String
      A selector to filter the elements that trigger the event.
    • eventType
      Type: String
      A string containing one or more space-separated JavaScript event types, such as "click" or "keydown," or custom event names.
    • handler
      Type: Function( Event eventObject )
      A function to execute at the time the event is triggered.

  • version added: 1.4.2.delegate( selector, eventType, eventData, handler )

    • selector
      Type: String
      A selector to filter the elements that trigger the event.
    • eventType
      Type: String
      A string containing one or more space-separated JavaScript event types, such as "click" or "keydown," or custom event names.
    • eventData
      Type: Anything
      An object containing data that will be passed to the event handler.
    • handler
      Type: Function( Event eventObject )
      A function to execute at the time the event is triggered.

  • version added: 1.4.3.delegate( selector, events )

    • selector
      Type: String
      A selector to filter the elements that trigger the event.
    • events
      A plain object of one or more event types and functions to execute for them.

As of jQuery 3.0, .delegate() has been deprecated. It was superseded by the .on() method since jQuery 1.7, so its use was already discouraged. For earlier versions, however, it remains the most effective means to use event delegation. More information on event binding and delegation is in the .on() method. In general, these are the equivalent templates for the two methods:

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// jQuery 1.4.3+
$( elements ).delegate( selector, events, data, handler );
// jQuery 1.7+
$( elements ).on( events, selector, data, handler );

For example, the following .delegate() code:

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$( "table" ).delegate( "td", "click", function() {
  $( this ).toggleClass( "chosen" );
});

is equivalent to the following code written using .on():

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$( "table" ).on( "click", "td", function() {
  $( this ).toggleClass( "chosen" );
});

To remove events attached with delegate(), see the .undelegate() method.

Passing and handling event data works the same way as it does for .on().

Additional Notes:

  • Since the .live() method handles events once they have propagated to the top of the document, it is not possible to stop propagation of live events. Similarly, events handled by .delegate() will propagate to the elements to which they are delegated; event handlers bound on any elements below it in the DOM tree will already have been executed by the time the delegated event handler is called. These handlers, therefore, may prevent the delegated handler from triggering by calling event.stopPropagation() or returning false.

Examples:

Click a paragraph to add another. Note that .delegate() attaches a click event handler to all paragraphs - even new ones.

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<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>delegate demo</title>
  <style>
  p {
    background: yellow;
    font-weight: bold;
    cursor: pointer;
    padding: 5px;
  }
  p.over {
    background: #ccc;
  }
  span {
    color: red;
  }
  </style>
  <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
 
<p>Click me!</p>
 
<span></span>
 
<script>
$( "body" ).delegate( "p", "click", function() {
  $( this ).after( "<p>Another paragraph!</p>" );
});
</script>
 
</body>
</html>

Demo:

To display each paragraph's text in an alert box whenever it is clicked:

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$( "body" ).delegate( "p", "click", function() {
  alert( $( this ).text() );
});

To cancel a default action and prevent it from bubbling up, return false:

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$( "body" ).delegate( "a", "click", function() {
  return false;
});

To cancel only the default action by using the preventDefault method.

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$( "body" ).delegate( "a", "click", function( event ) {
  event.preventDefault();
});

Can bind custom events too.

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<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>delegate demo</title>
  <style>
  p {
    color: red;
  }
  span {
    color: blue;
  }
  </style>
  <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
 
<p>Has an attached custom event.</p>
<button>Trigger custom event</button>
<span style="display:none;"></span>
 
<script>
$( "body" ).delegate( "p", "myCustomEvent", function( e, myName, myValue ) {
  $( this ).text( "Hi there!" );
  $( "span" )
    .stop()
    .css( "opacity", 1 )
    .text( "myName = " + myName )
    .fadeIn( 30 )
    .fadeOut( 1000 );
});
$( "button" ).click(function() {
  $( "p" ).trigger( "myCustomEvent" );
});
</script>
 
</body>
</html>

Demo: