Wednesday, July 18, 2012

JavaScript - Singleton Pattern

The singleton design pattern is probably the simplest and most common pattern in JavaScript.

So why should you use the singleton pattern?
  • Encapsulation of members & functions
  • Creates its own Namespace
  • A singleton is a single instance object
  • Encourages code reuse
  • Improves readability because you can logically organise your code

The point of a singleton is to only have one instance. A shopping cart is a good example of something that you may want only a single instance of at one time.


The simplest form of Singleton is an object literal. This loose form of Singleton cannot be instantiated. All of the members are now accessible through the Singleton variable, accessible through dot notation.
varmyCart = {
   self: this,

   totalCost: 0,

   totalQty: 0,

   cart: {},

   getCart: function(){ },

   updateCart: function(){ }

};

alert( "Total cost: $"+ myCart.totalCost );

By using closures, we can create Private and Public Members and Functions. This pattern is more commonly called the Module Pattern.

 var myCart = function(){
    // Private

    var self = this;

    var totalCost = 0;

    var totalQty = 0;

    var cart = {};

    return {

        // Public

        getCart: function(){ },

        updateCart: function(){ }

    };

}();