// source http://jsbin.com/dovoru

Emitter.js

function _Emitter (name) {
  this.callers = {};
}

  _Emitter.prototype.add = function () {
    this.callers[this.name] = true;
  };

  _Emitter.prototype.log = function () {
    console.log(JSON.stringify(this.callers));
  };

// inherited
  
function Emitter (name) {
  this.name = name;
}

Emitter.prototype = new _Emitter();

// tests
  
var common = new Emitter(),
    foo = new Emitter('foo'),
    bar = new Emitter('bar');

foo.add();
bar.add();

common.log();


// 
// Recource.on('update', '087td08d7t0d78td073y3y893y', function () {});
// 
// Recource.on('update', 'any', function () {});
//

console output:

"{"foo":true,"bar":true}"