delegate and on methods In jQuery

delegate method

Earlier, I mentioned that the method bindonly adds event handlers to elements that already exist in the DOM structure at the time of its action. When adding new elements, for example, using a method, appendtheir events will not be processed.

But jQuery provides a special method delegatethat allows you to create and register handlers for future elements that aren’t already in the DOM structure. This method has the following use cases:

delegate(‘selector’,’event’, event_handler): Adds a handler for the event. A selector is used to filter the elements for which a handler is added.

delegate(‘selector’,’event’, eventdata, eventhandler): same as above, plus a parameter to pass the event data to the Event object (

Using the delegate method:


<script type="text/javascript">
    $('body').delegate('button','click', function(e){
        $(this).css('color', 'red');
        alert('Button handler: '+$(this).text());

Here, for all elements buttonthat are in the element body, a click handler is added. And despite the fact that after that a new button is added, a handler will also work for it.

We can also unregister the event handler with the undelegate:


on method

The method onwas introduced in jQuery 1.7 and is in many ways a replacement for the delegate method and has the same effect. It has similar usage forms:

on(‘event’, ‘selector’, event_handler)

on(‘event’, ‘selector’, event_data, event_handler)

In fact, compared to the delegate method, in this case, only the selector and event parameters change:

$('body').on('click', 'button', function(e){
    $(this).css('color', 'red');
    alert('Button handler: '+$(this).text());

To unregister event handlers, you can use the method off:

// remove click event handlers for buttons
// remove all handlers for elements inside the body tag