よく使うものだけまとめる

Ym.js

function Ym (obj) {
   // Ym() returns an instance of this Constructor
   var Constructor = function (obj) {
     if (obj)
       for (key in obj)
         if (obj.hasOwnProperty(key))
           this[key] = obj[key]
   }
   // Copy the prototype of the object given to our Ym object's prototype
   // javascript 1.8.2 or lator
   if (obj) Constructor.prototype = Object.getPrototypeOf(obj); 
  
   // Keep the event listener maps
   var listenerStack = []; //for event emitter

   // You know what it does
   Constructor.prototype.each = function (fn) {
     for (key in this) 
       if (this.hasOwnProperty(key))
         fn(this[key], key);
     return this;
   },

   // Register an event listener
   Constructor.prototype.on = function (ev, listener) {
     listenerStack.push({name : ev, listener : listener});
     return this;
   },
   // Unset an event listener
   Constructor.prototype.off = function (ev, listener) {
     Ym(listenerStack).each(function (item, key) {
         if (item && item.name === ev && item.listener === listener) listenerStack[key] = undefined;
     });
     return this;
   },
   // Emit listeners that are listening for this event
   Constructor.prototype.fire = function (ev, obj) {
     obj = obj || {};
     Ym(listenerStack).each(function (item) {
       if (item && item.name == ev) item.listener(obj);
     });
     return this;
   },

   // The first argument passed will extend an instance of Ym
   // The second argument passed will extend the prototype of Ym
   // *There should be a better notation
   Constructor.prototype.extend = function (my, proto) {
    var self = this; 
    Ym(my).each(function (item, key) {
       self[key] = item;
     });
     Ym(proto).each(function (item, key) {
       Constructor.prototype[key] = item;
     });
     return this;
   }

   return new Constructor(obj);
}

Ym_test.js

[
  (function () {
    var a = 0;
    Ym().on('ev', function (e) {a = e}).fire('ev', 1);
    return a;
  })() === 1,
  (function () {
    var a = 0, f;
    Ym().on('ev', f = function (e) {a = e}).off('ev', f).fire('ev', 1);
    return a;
  })() === 0,
  Ym({a:1}).extend({b:2},{addAB : function () {return this.a + this.b}}).addAB() === 3 
] 

mapやkeysはべつにあとからextendすればいいやと思って消しました