Singleton Design Pattern

This Javascript program demonstrates a singleton design pattern. The constructor function prevents multiple instances from being created. The static GetInstance() provides global access to the singleton instance.

Singleton.html

<!DOCTYPE html>
<html>
  <head>
    <title>XoaX.net's Javascript</title>
    <script type="text/javascript" src="Singleton.js"></script>
  </head>
  <body onload="Initialize()">
  </body>
</html>

Singleton.js

class CSingleton {
	// The singleton instance, a private class memeber.
	static #sqInstance;
	constructor() {
		if (!CSingleton.#sqInstance) {
			CSingleton.#sqInstance = this;
		} 
		return CSingleton.#sqInstance;
	}
	static GetInstance() {
		if (!CSingleton.#sqInstance) {
			CSingleton.#sqInstance = new CSingleton();
		}
		return CSingleton.#sqInstance;
	}
}

function Initialize() {
	var qSingleton1 = CSingleton.GetInstance();
	var qSingleton2 = new CSingleton();
	var qSingleton3 = new CSingleton();
	var qSingleton4 = CSingleton.GetInstance();
	document.writeln("Instances are equal: " + (qSingleton1 === qSingleton2)+"<br />");
	document.writeln("Instances are equal: " + (qSingleton1 === qSingleton3)+"<br />");
	document.writeln("Instances are equal: " + (qSingleton1 === qSingleton4)+"<br />");
}

Core JavaScript

Singleton Design Pattern

Singleton.html

Singleton.js

Output