Comments on: Object-Oriented JavaScript Tip: Implementing the Singleton Pattern

By: fred

fred — Sun, 28 Mar 2010 16:01:59 +0000

Why not just using

Singleton = function() {
// private vars and functions
return {
// public vars and functions
 
}();

When the code run, the Singleton is automatically instantied an could not be instantied a second time
(except if used with var Second = new Singleton.constructor())

}();

By: Anthony

Anthony — Sun, 28 Mar 2010 08:15:59 +0000

It bothers me that (Class.Singleton() !== (new Class())) so I figured out how to stop instantiation of the class without disrupting the way it works… here it is:

var Test = new function Test()
{
	if ( Test.initialized )
		throw new Error('You may not instantiate Test');
 
	var instance = this;
 
	Test.Singleton = function() { return instance; };
	return Test;
};
Test.initialized = true;
Test.prototype.data = 'some data';
 
var obj = Test.Singleton();
alert(obj.data);
obj.data = 'test';
alert(obj.data);
 
var other = Test.Singleton();
alert(other.data);
 
var fail = new Test;
alert(fail.data);

By: Ans

Ans — Mon, 23 Nov 2009 21:00:29 +0000

Hi Daniel,

If I understand the question correctly, it’s the variable. Notice “new Singleton();” and “Singleton.getInstance();” won’t work if the variable name is changed, however, they don’t care if the constructor function name is changed (as long as it is consistent within the function definition itself).

By: Daniel

Daniel — Mon, 23 Nov 2009 20:22:13 +0000

in the line “var Singleton = new function Singleton() ”

when Singleton.getInstance is called, is the variable or function Singleton being dereferenced?