var Adder = function(a, b) {
	this.a = a;
	this.b = b;
};
Adder.prototype.add = function() {
	return this.a + this.b;
};
module.exports = Adder;
--> node
> Var Adder = require('./adder');
> Adder [Function]
> var adder = new Adder(1,2);
> adder {object}
> adder.__proto__ { add: [Function] }

---------- 2. Add default --------
var Adder = function(a, b) {
	this.a = a;
	this.b = b;
};
Adder.prototype.coalesce = function() {
	if(! this.a) { this.a = 0; }
	if(! this.b) { this.b = 0; }
};
Adder.prototype.add = funciton() {
	this.coalesce();
	return this.a + this.b;
}
module.exports = Adder;

--> node
> var Adder = require('./adder');
> var adder = new Adder(1);
> adder.add()
> adder.__proto__.coalesce = funciton() {}
> adder.add()
> adder.a
------ 3. Avoid expose: closure -----
var Adder = function(a, b) {
	function coalesce() {
		if(! a) { a = 0; }
		if(! b) { b = 0; }
	};
	this.add = function() {
		coalesce();
		return a + b;
	}
};
module.exports = Adder;
--> node
> var Adder= require('./adder');
> var adder = new Adder(1,2);
> adder
> adder.add();

----- 4. Remove new: return {} ------
var Adder = function(a, b) {
	function coalesce() {
		if(! a) { a = 0; }
		if(! b) { b = 0; }
	};
	function add() {
		coalesce();
		return a + b;
	}
	return {
		add: add
	};
};
module.exports = Adder;
--> node
> var Adder= require('./adder');
> var adder = Adder(1,2);
> adder.__proto__
> adder.add()

----- 5. working with Node's modules as an event emitter ------
var EventEmitter = require('events').EventEmitter;
var Adder = function(a, b) {
	var that;
	function coalesce() {
		if(! a) { a = 0; }
		if(! b) { b = 0; }
	};
	function add() {
		coalesce();
		that.emit('add', a, b);
		return a + b;
	}
	that {
		add: add
	};
	that.__proto__ = EventEmitter.prototype;
	return that;
};
-->node
> var Adder = require('./adder');
> var adder = Adder(1,2)
> adder.on('add', function(a,b) {
	console.log('ADDING', a, 'and', b);
});
> adder.add();