Ask if event has listener in jQuery

Question

A function triggers an event and passes on some data which then will possibly be processed by a listener. If not, the function wants to process the data by herself. Well, as I don't know if the package was handled or not, my idea was to find out if there is a listener at all. Is there a way to do this or does anyone have better ideas to my problem?

Thanks in advance!

Looks like that's a plugin: https://github.com/sebastien-p/jquery.hasEventListener — Barmar, May 12 '13 at 09:02
All events are binded to some elements. So in Chrome you have developer tools -> elements tab -> event listeners tab (in right side). Guess there is something similar in other browsers' devtools. — zelibobla, May 12 '13 at 09:04
This answere seems to show do what you want: http://stackoverflow.com/a/1515073/355499 — Emil L, May 12 '13 at 09:16
Thanks all for you help. I then solved the problem by checking the lenght of the `$.data('events')` array. — quape, May 12 '13 at 15:31

score 2 · Accepted Answer · answered May 12 '13 at 09:15

You can to this with jQuery prior to 1.8 like this:

<script src="http://code.jquery.com/jquery-1.6.min.js"></script>

<script>
$(document).ready(function() {

$("#click_here").click(function() {
  alert("Handler for .click() called.");
});

 console.log( $('#click_here').data('events') );

});

</script>

<div id="click_here">Click here</div>

score 1 · Answer 2 · answered Jul 15 '13 at 10:08

I created a plugin mainly to be used in your tests.

// Example usage
$('.foo').hasEvent('click', someHandler) 
// returns true if someHandler is bound via jQuery on '.foo' 
// for the click event

The plugin is tested to work with jQuery 1.7 and up

The plugin is hosted on github

score 1 · Answer 3 · answered Dec 14 '14 at 09:14

I had a VERY similar problem. It's never been something that's been properly supported in jquery and instead was kind of a hack. So you could do it prior to version 1.8 in jquery by using

data('events')

After 1.8, you can use:

$._data( $('.element')[0], 'events' );

BUT if you're trying to do what I was doing... make sure an event handler is only assigned once on a control (i.e. a save button after some form validation), then you can either:

Add a class and remove it to indicate whether an element has an event (ugly).
Remove any handers before assigning it i.e.

$('element').unbind('event'); $('element').on('click', save);

Ask if event has listener in jQuery

3 Answers3