JavaScript, stop additional event listeners

Question

Imagine I have this code:

var myFunc1 = function(event) {
    alert(1);
}
var myFunc2 = function(event) {
    alert(2);
}

element.addEventListener('click', myFunc1);
element.addEventListener('click', myFunc2);

When the click event is fired myFunc1 is called, then myFunc2. But how do I (if at all possible) stop myFunc2 from being called if some condition in myFunc1 is met? event.stopPropagation() is not the solution, as this is not an event capturing/bubbling problem.

Thanks.

Answer 1

I'll start with the simplest answer that satisfies the constraints you've given so far. If it doesn't meet some condition you haven't yet specified, let me know and I'll update it.

Only allow one click handler, and call functions based on conditions there. Your test code becomes:

var myFunc1 = function(event) {
    alert(1);
}
var myFunc2 = function(event) {
    alert(2);
}
var clickHandler = function(event) {
    if (f1active) myFunc1(event);
    if (f2active) myFunc2(event);
}

element.addEventListener('click', clickHandler);
var f1active = true;
var f2active = true;

and you can of course put any conditions you want to in clickHandler.

Answer 2

Still looking for a better solution, but this may be the only way to do it:

var myFunc1 = function(event) {
    alert(1);
    if (something) {
     event.cancel = true;
    }
}
var myFunc2 = function(event) {
    if (event.cancel) {
     return;
    }
    alert(2);
}

document.body.addEventListener('click', myFunc1, false);
document.body.addEventListener('click', myFunc2, false);

Thoughts/comments welcome.

Answer 3

The DOM Level-3 method event.stopImmediatePropagation is exactly what I need here, unfortunately it's not currently implemented in any browser (that I know of).

http://www.w3.org/TR/2003/NOTE-DOM-Level-3-Events-20031107/events.html#Events-Event-stopImmediatePropagation

Answer 4

There's a further problem: the order that event listeners are executed is undefined. You'll need to handle event dispatch on your own to get around this, which leads us to some variant of llimllib's suggestion.

function dispatchSleightEvent(evt) {
    var listeners = evt.currentTarget.sleightListeners[evt.type];
    // can't use for-in because enumeration order is implementation dependent
    for (var i=0; i<listeners.length; ++i) {
       if (listeners[i]) {
         if (! listeners[i].call(evt.currentTarget, evt)) {
           return false;
         }
       }
    }
    return true;
}

function mixinSleightTarget(obj) {
  if (! obj.sleightListeners) {
    obj.sleightListeners = {}
    obj.addSleightListener = function(type, listener) {
        if (!this.sleightListeners[type]) {
            this.sleightListeners[type] = [];
            this.addEventListener(type, dispatchSleightEvent);
        }
        if (!this.sleightListeners[type+listener] {
          this.sleightListeners[type+listener] = this.sleightListeners[type].length;
          this.sleightListeners[type].push(listener);
        }
    }
    obj.removeSleightListener = function(type, listener) {
        if (this.sleightListeners[type+listener] {
          delete this.sleightListeners[type][this.sleightListeners[type+listener]];
          delete this.sleightListeners[type+listener];
        }          
    }
  }
}

This code is completely untested. To stop event dispatch while on a single target, an event listener returns false. If you want more data hiding, you can rewrite the above from a functional programming standpoint, though this might introduce memory leaks.

Answer 5

Hi Jack, I second the outis solution, sounds like you need to decorate or adapt the existing DOM event dispatching model with your own event dispatcher.

Did some searching and found this link, which may or may not suit your needs, based on an actionscript dispatcher implementation, dated 2007.

http://positionabsolute.net/blog/2007/06/event-dispatcher.php

Of course I'm not really a javascripter, so give me a heads up if this is not relevant.