emitter.js

// In Chrome Canary, with Experimental JavaScript enabled...

(function( exports ) {
  // Create a reusable symbol for storing
  // Emitter instance events

  var sym = new Symbol();

  function Emitter() {
    this[ sym ] = {
      events: {}
    };
  }

  Emitter.prototype.on = function( type, handler ) {
    var events = this[ sym ].events;

    if ( !events[ type ] ) {
      events[ type ] = [];
    }
    events[ type ].push( handler );
    return this;
  };

  Emitter.prototype.off = function( type, handler ) {
    var events = this[ sym ].events[ type ];

    if ( events ) {
      if ( !handler ) {
        events.length = 0;
      } else {
        events.splice( events.indexOf(handler), 1 );
      }
    }
    return this;
  }

  Emitter.prototype.emit = function( type, data ) {
    var event, events;

    events = (this[ sym ].events[ type ] || []).slice();

    if ( events.length ) {
      while ( event = events.shift() ) {
        event.call( this, data );
      }
    }
    return this;
  }
  exports.Emitter = Emitter;
}(this));


function Serial( path ) {
  this.path = path;
}

function Device( path ) {
  Emitter.call( this );
  this.serial = new Serial( path );
}

Device.prototype = Object.create( Emitter.prototype );

function handler( data ) {
  console.log( "signal", data );
}

var device = new Device();


device.on( "signal", handler );
device.on( "signal", function() { console.log( 1 ); });
device.on( "signal", function() { console.log( 2 ); });
device.on( "signal", function() { console.log( 3 ); });
// Will trigger 4 events.
device.emit( "signal", { a: "alpha", b: "beta" });

device.off( "signal", handler );

// Will trigger 3 events.
device.emit( "signal", { a: "alpha", b: "beta" });

console.log( device );

// Device {
//   serial: Serial { path: ... },
//   on: function,
//   off: function,
//   emit: function
// }

// Note that the "device" instance does not have any data
// properties that were inherited by Emitter--only the inherited
// API from Emitter.prototype and it's own properties