'use strict';
  
  var forEach    = require('es5-ext/object/for-each')
    , validValue = require('es5-ext/object/valid-object')
  
    , push = Array.prototype.apply, defineProperty = Object.defineProperty
    , create = Object.create, hasOwnProperty = Object.prototype.hasOwnProperty
    , d = { configurable: true, enumerable: false, writable: true };
  
  module.exports = function (e1, e2) {
  	var data;
  	(validValue(e1) && validValue(e2));
  	if (!hasOwnProperty.call(e1, '__ee__')) {
  		if (!hasOwnProperty.call(e2, '__ee__')) {
  			d.value = create(null);
  			defineProperty(e1, '__ee__', d);
  			defineProperty(e2, '__ee__', d);
  			d.value = null;
  			return;
  		}
  		d.value = e2.__ee__;
  		defineProperty(e1, '__ee__', d);
  		d.value = null;
  		return;
  	}
  	data = d.value = e1.__ee__;
  	if (!hasOwnProperty.call(e2, '__ee__')) {
  		defineProperty(e2, '__ee__', d);
  		d.value = null;
  		return;
  	}
  	if (data === e2.__ee__) return;
  	forEach(e2.__ee__, function (listener, name) {
  		if (!data[name]) {
  			data[name] = listener;
  			return;
  		}
  		if (typeof data[name] === 'object') {
  			if (typeof listener === 'object') push.apply(data[name], listener);
  			else data[name].push(listener);
  		} else if (typeof listener === 'object') {
  			listener.unshift(data[name]);
  			data[name] = listener;
  		} else {
  			data[name] = [data[name], listener];
  		}
  	});
  	defineProperty(e2, '__ee__', d);
  	d.value = null;
  };