EventEmitter

EventEmitter.js

var EventEmitter = (function() {

  var cache = new WeakMap();

  function EventEmitter() {
    cache.set( this, {} );
  }

  EventEmitter.prototype = {
    
    on: function( evt, fn ) {
      var hash = cache.get( this );
      ( hash[ evt ] || ( hash[ evt ] = [] ) ).push( fn );
      return this;
    },

    emit: function( evt ) {
      var args = Array.prototype.slice.call( arguments, 1 ),
        events = cache.get( this )[ evt ],
        len, i;

      if ( events ) {
        for ( i = 0, len = events.length; i < len; ++i ) {
          events[ i ].apply( this, args );
        }
      }

      return this;
    },

    off: function( evt, fn ) {
      var hash = cache.get( this ), 
        events = hash[ evt ],
        keep, len, i;

      if ( !evt ) {
        cache.set( this, {} );
      }

      else if ( events && !fn ) {
        delete hash[ evt ];
      }

      else if ( events ) {
        keep = [];
        for ( i = 0, len = events.length; i < len; ++i ) {
          if ( events[ i ] !== fn ) {
            keep.push( events[ i ] );
          }
        }
        hash[ evt ] = keep;
      }

      return this;
    }

  };

  return EventEmitter;

}());