Module - The Good Parts

module.js

var serial_maker = function () {
	// Produce an object that produces unique strings. A
	// unique string is made up of two parts: a prefix
	// and a sequence number. The object comes with
	// methods for setting the prefix and sequence
	// number, and a gensym method that produces unique
	// strings.
	var prefix = '';
	var seq = 0;
	return {
		set_prefix: function (p) {
			prefix = String(p);
		},
		set_seq: function (s) {
			seq = s;
		},
		gensym: function ( ) {
			var result = prefix + seq;
			seq += 1;
			return result;
		}
	};
};
var seqer = serial_maker();
seqer.set_prefix = ('Q');
seqer.set_seq = (1000);
var unique = seqer.gensym(); // unique is "Q1000"

//The module pattern takes advantage of function scope and closure to create relationships 
//that are binding and private.
//The general pattern of a module is a function that defines private variables and functions; 
//creates privileged functions which, through closure, will have access to 
//the private variables and functions; and that returns the privileged functions or stores them in an accessible place.
//Use of the module pattern can eliminate the use of global variables. It promotes
//information hiding and other good design practices. It is very effective in encapsulating applications and other singletons.
//It can also be used to produce objects that are secure. Let’s suppose we want to make
//an object that produces a serial number.

//The methods do not make use of 'this' or 'that'. As a result, there is no way to compromise the 'seqer'. 
//It isn’t possible to get or change the prefix or seq except as permitted by the methods. The 'seqer' object is mutable, so the methods could be
//replaced, but that still does not give access to its secrets. 'seqer' is simply a collection
//of functions, and those functions are capabilities that grant specific powers to use or
//modify the secret state.
//If we passed 'seqer.gensym' to a third party’s function, that function would be able to
//generate unique strings, but would be unable to change the 'prefix' or 'seq'.