Implementing Element.hasEvent in MooTools 1.2.3
MooTools allows you to easily add event listeners to elements using the addEvent and removeEvent methods. One thing MooTools doesn't have is a hasEvent method which will check an element's list of listeners to see if the element has been assigned a specific function per event. I experimented with implementing this functionality and believe I've found the best solution.
The MooTools JavaScript
Element.implement({
hasEvent: function(eventType,fn) {
//get the element's events
var myEvents = this.retrieve('events');
//can we shoot this down?
return myEvents && myEvents[eventType] && (fn == undefined || myEvents[eventType].keys.contains(fn));
}
});
The code is quite short. I can't provide a great use case for implementing this in the MooTools Core but it's a lovely little snippet to have at your disposal.
![How to Create a Twitter Card]()
One of my favorite social APIs was the Open Graph API adopted by Facebook. Adding just a few META tags to each page allowed links to my article to be styled and presented the way I wanted them to, giving me a bit of control...
![An Interview with Eric Meyer]()
Your early CSS books were instrumental in pushing my love for front end technologies. What was it about CSS that you fell in love with and drove you to write about it?
At first blush, it was the simplicity of it as compared to the table-and-spacer...
![jQuery Random Link Color Animations]()
We all know that we can set a link's :hover color, but what if we want to add a bit more dynamism and flair? jQuery allows you to not only animate to a specified color, but also allows you to animate to a random color.
The...
![Disable Autocomplete, Autocapitalize, and Autocorrect]()
Mobile and desktop browser vendors do their best to help us not look like idiots by providing us autocomplete, autocorrect, and autocapitalize features. Unfortunately these features can sometimes get in the way; we don't always want or need the help they provide. Luckily most browsers allow...
anything related with Jquery? i’ve looking for this so much time…
Hey cool one, I admit I had wished I had such a function a few times
You need to check that the retrieved events storage isn’t undefined when no events at all are defined. “retrieve” only returns a default object if one is provided using the second parameter.
var myEvents = this.retrieve('events'); return myEvents && myEvents[eventType] && (fn == undefined || myEvents[eventType].keys.contains(fn));Generally it’s a good idea to apply “tell, don’t ask” pattern. But if you’re making plugins that should operate together with other implementations it can be really useful to check for the existence of subscribers to ensure compatibility.
Awesome. I made one myself a while back (before 1.2.3)
Native.implement([Element, Window, Document, Events], { /* used to check if a type of event has been set */ hasEvent: function(type) { try { var evs = this.retrieve('events', {}); if(!evs || !evs[type]) return false; return true; } catch(err) { return $chk(this.$events[type]); } } });Very handy. Thanks.
hey, I just needed a function to do that today and I thought “Didn’t Dave Walsh post something like that a while back?”. Bingo! Thanks a lot, saved me some time.
Really helpful, I was getting mad with a function giving a click event once and again to a div :S
Thanks David!!!
this is so killer.
Great stuff! I’ll be using this in my tests for assertions.
I just realized that I needed to change:
to
(I added
$chk) in order to get it to work when no events are defined.A use I suppose you could say for this is an idea I’ve been entertaining if I knew anyone who could help me code the core would be for a forum system highly relying on AJAX and DHTML. When you load a new link into the body, it by nature has no events caught to it, so you need to look through all links pointing to something like a forum post, etc, and add the event. but you don’t want to double up on the events, as it could become a hassle if you want to log information through ajax (… not a good idea if you ask me, but I’m sure someone would), so checking to see if it’s already got the function within its events would be an awesome sort of thing to do.
Just a thought. Pretty sure someone else will poke HUGE holes in my logic here.