JavaScript Singleton Design Pattern

The Singleton pattern restricts an instantiation of an object to a single instance thus reducing its memory allocation and allowing a "lazy loading" on an as-needed basis. The advantages of that pattern are the reduced memory occupation, single point of access and a postponed initialization which prevents instantiation until it is required. As a disadvantage one may point out that object is hardly ever reset once instantiated and sometimes there might be hidden dependencies.

<script type="text/javascript">

var singleton = ( function(window) {

  function init() {
    function action1() {
      console.log("Action1");
    }
    function action2() {
      console.log("Action2");
    }
    return {
      action1 : action1,
      action2 : action2
    };
  }
 
  if(!window._instance) {
      window._instance = new init();
  }
  return window._instance;

} )( window );

singleton.action1(); // action1 is called
singleton.action2(); // action2 is called

</script>

Another interesting singleton pattern implementation is the following:

<script type="text/javascript">

   var Singleton = function() {
        if (window._instance) {
	        return window._instance;			
        }
        this.init();
	    window._instance = this;
    };
    Singleton.prototype = {
        init: function() {
            this.value = 5;
        },
	    getValue: function() {
		    return this.value;
	    }
    };

    var singleton = new Singleton();
    console.log(singleton.getValue());

</script>