JavaScript/Notes/Singleton

From Noisebridge
Jump to navigation Jump to search
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

Singleton with information hiding.

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>

The function scope allows us to hide variable `b`. jsbin

An object literal does not allow information hiding: <source lang="javascript"> // exposed variables. var a = 3; var b = a + 2; var anObject = {

 name : b;

}; </source>

Example: APE Animation Manager