Hoopla

An event dispatcher for JavaScript that knows its priorities.

Node's event-emitter package is fine for simple events, but if you get more than a few listeners to a single event, it becomes difficult to manage. Hoopla allows you to set priorities for your event handlers so they get called in a certain order.

Creating a dispatcher

var Hoopla = require('hoopla');
var dispatcher = new Hoopla();

Basic events

Add listeners with the addListener method and fire events with dispatch.

dispatcher.addListener('init', function() {
    console.log('it was initialized!');
});
 
dispatcher.dispatch('init');
// Prints 'it was initialized!'

Event priority

Hoopla allows you to set an unlimited number of event listeners for any event. By default, they all have a priority of 0, so they get handled in the order they are registered. If you give a handler a negative or positive priority, Hoopla will call the handlers in order from least to greatest.

dispatcher.addListener('init', function() {
    console.log('default init handler');
});
 
dispatcher.addListener('init', function() {
    console.log('early init handler');
}, -5);
 
dispatcher.addListener('init', function() {
    console.log('late init handler');
}, 3);
 
dispatcher.dispatch('init');
// Prints 'early init handler', 'default init handler', 'late init handler'

Event objects

Hoopla passes an Event object to your event listeners. Events are objects that have a name, and attributes.

dispatcher.addListener('route', function(event) {
    if (event.getName() === 'route') {
        console.log(event.get('foo'));
    } else {
        event.set('foo', 3);
    }
});

If you pass an object as the second argument to dispatch, Hoopla will set its properties as attributes on the event object.

dispatcher.addListener('init', function(event) {
    console.log(event.get('foo')); // prints 'foo value'
});
 
dispatcher.dispatch('init', {foo: 'foo value'});

Stopping propagation

Event listeners can stop propagation for an event meaning that event will not trigger any more listeners.

dispatcher.addListener('init', function(event) {
   event.stopPropagation();
});
 
dispatcher.addListener('init', function() {
    // will not be called
}, 1);
 
dispatcher.dispatch('init');

Creating an event object

If you wish, you can create an event object manually and pass it to the dispatch method.

// Create an event with dispatcher.createEvent
var eventA = dispatcher.createEvent('foo', {a: 'a'});
// or create an event with the Event constructor
var eventB = new Hoopla.Event('bar', {b: 'b'});
 
dispatcher.dispatch(eventA);
dispatcher.dispatch(eventB);

You can create custom events objects. An event object must have getName and isPropagationStopped methods.

var fooEvent = {
    getName: function() {
        return 'foo';
    },
    isPropagationStopped: function() {
        return false;
    }
};
dispatcher.dispatch(fooEvent);