events.coffee

@events =

  events: {}

  on: (topic, handler, context = this) ->
    (@events[topic] or= []).push {handler, context}

  trigger: (topic, args...) ->
    return unless @events[topic]?
    handler.apply(context, args) for {handler, context} in @events[topic]

events.js

(function() {

  var slice = Array.prototype.slice;

  this.events = {

    events: {},

    on: function (topic, handler, context) {
      if (context == null) context = this;
      this.events[topic] = this.events[topic] || []
      this.events[topic].push({ handler: handler, context: context });
    },

    trigger: function (topic) {
      if (this.events[topic] == null) return;
      var args = slice.apply(arguments, 1);
      for (var i = 0, l = this.events[topic].length, event; i < l; i++) {
        event = this.events[topic][i];
        event.handler.apply(event.context, args);
      }
    }
  };

}).call(this);

Destructured assignment in a for ... in looks awesome, thanks for the example.

One small issue: trigger is now going to collect the return values of handler. Add an undefined or null as the last expression of trigger.

It would be better to add return statement, so methods will return nothing. If we add undefined or null the methods will contain return undefined or return null in their JavaScript presentation.

Something like this would be more correct (like source JS code)

@events =

  events: {}

  on: (topic, handler, context = this) ->
    (@events[topic] or= []).push {handler, context}; return

  trigger: (topic, args...) ->
    return unless @events[topic]?
    handler.apply(context, args) for {handler, context} in @events[topic]; return

Yeah, I'm well aware of implicit returns guys; I'd return this if I cared, but don't :)