JavaScript/Notes/Singleton

Singleton with information hiding.

Constructors

Before going over Singleton patterns, lets first take a look at how constructors work.

Lazy Initialization

This example of a Singleton uses my patented "function rewriting" technique, where `getAnObject` is identifier is reassigned to the nested closure. <source lang="javascript"> function getAnObject(a) {

 var anObject;

 var b = a + 1;

 return (getAnObject = function() {
   if(! anObject ) {
     anObject = {name: b};
   }
   return anObject;
 })();

} </source>

Eager Initialization

Not a Singleton, but a constructor. <source lang="javascript"> // Not a Singleton. var C = function(a) {

 var b = a + 2;
 this.name = b;

};

var o1 = new C(3); var o2 = new C(4); var o3 = new C(5); </source>

Example: Constructors and prototype inheritance. jsbin

Singleton: <source lang="javascript"> var anObject = new function(a) { // hidden variables.

 var b = a + 2;
 this.name = b;

}(3);

alert(anObject.name); alert(typeof b); // "undefined" </source>

Function scope allows us to hide variable `b`. jsbin

Object literal notation does not provide any information hiding mechanism: <source lang="javascript"> // exposed variables. var a = 3; var b = a + 2; var anObject = {

 name : b;

}; </source>

Example: APE Animation Manager