once doesn't always work

[nathggns]

In some situations, a once event gets fired multiple times.

I haven't yet made a reproducible test case for this, but I've seen it happen and cause bugs in projects of mine.

[nathggns]

Code like the following

describe('play button', function() {
    it('should work', function(done) {
        var state = player.playing();

        console.log('-');

        player.once('track.toggle', function() {

            console.log('.');

            assert(player.playing()).not().equals(state);
            var newState = player.playing();

            player.once('track.toggle', function() {
                assert(player.playing()).not().equals(newState);
                assert(player.playing()).equals(state);

                done();
            });

            $el.find('[data-button=play]').click();
        });

        $el.find('[data-button=play]').click();
    });
});

results in this in the log.

[nathggns]

Managed to reduce the test case to this.

var ee = new EventEmitter();
var counter = document.querySelector('#count');
var count = 0;
ee.once('foo', function() {
  counter.innerHTML = ++count;
  this.trigger('foo');
});

ee.trigger('foo');

Demo

[Olical]

Am I correct in saying that if you recursively execute a once listener it will be called twice and only twice? If that is the case then it should be fixed by removing once listeners before they are executed. It seems a little bit weird to me, but that will probably be the only way.

[nathggns]

No, that test case I showed you will run until there is a StackOverflow. The reason mine only ran twice was because of the way I ended up triggering the event inside of the listener.

However, it will be fixed by removing the once listener before it is triggered.

[Olical]

Okay got it, should still be able to fix it in the same way though. Thanks for bringing this up, looking into it now.

[Olical]

Fixed and releasing now. I don't like repeating the removal line but it is a necessary evil at the moment. I was thinking of adding a partial application function and creating a removal variable which can be executed when required. That would save duplicating any arguments and function calls but it seems like overkill for such a trivial change.

I'll just live with it for now. I can restructure in the future when the API is even more mature and I know what users actually want.

[nathggns]

Awesome, thanks mate.