A Pub/Sub API (Originally written for Gaia)

EventEmmiter.js

 this.EventEmmiter = (function() {

  var events = {};
  var UUID = -1;

  // Function to publish/trigger events
  function trigger(evt, args) {

    if (!events[evt]) {
      return false;
    }

    var subscribers = events[evt];
    var len = 0;
    if (subscribers) {
      len = subscribers.length;
    }

    while (len--) {
      subscribers[len].callback(evt, args);
    }
    return true;
  }

  // Function to subscribe to events
  function on(evt, callback) {

    if (!events[evt]) {
      events[evt] = [];
    }

    var token = (++UUID).toString();
    events[evt].push({
      token: token,
      callback: callback
    });

    return token;
  }

  // Function to Unsubscribe
  // Token based unsubscription
  function off(token) {

    for (var evt in events) {
      if (events[evt]) {
        for (var i = 0; i < events.length; i++) {
          if (events[evt][i].token === token) {
            events[evt].splice(i, 1);
            return token;
          }
        }
      }
    }

    return false;
  }

  return {
    trigger: publish,
    on: subscribe,
    off: unsubscribe
  };
}());

Usage

• Subscribing to an event:

EventEmmiter.on(evt, callback);

evt: The event you want to subscribe to.

callback: The function to be called when that event occurs.

Example:

var sub = EventEmmiter.on('login', function(evt, args) {
  console.log(evt + 'occured, arguemnts supplied: ' + args);
});

Note: 'sub' is later used to unsubscribe from the event.

• Publishing an event:

EventEmmiter.trigger(evt, args);

evt: The event you want to publish.

args: Message to be passed to the listener

Example:

EventEmmiter.trigger('login', {
  'user': 'rolls'
});

The argument can be any valid JavaScript argument.

• Unsubscribing from an event:

EventEmmiter uses a token based unsubscription mechanism.

EvenEmmiter.off(token);

Example:

EventEmmiter.off(sub);

where sub is defined when subscribing to the event (See subscribe example)