ES6 Singleton

Singleton.js

// Singleton implemented abstractly in a Class

class Singleton {
	
	constructor() {
		var instance = ( Singleton._instance !== undefined ) ? Singleton._instance : this;
		Singleton._instance = instance;
		return instance;
	}
	
	static get instance() {
		return new Singleton();
	}
}


// Singleton as a static factory that mixes-in the instance reference to the target static class

class Singleton {
	
	getInstance( className ) {
		
		if ( !( className.__instance instanceof className ) ) {
			// could also check here if member __instance exists and warn/error/etc. if so
			className.__instance = new className();
		}
		
		return className.__instance;
	}
}


// Singleton as a static factory that keeps its own map of instances

class Singleton {
	
	static getInstance( className ) {
		
		if ( !Singleton.instances ) Singleton.instances = {}; 
		
		if ( !Singleton.instances[ className ] ) {
			Singleton.instances[ className ] = new className();
		}
		
		return Singleton.instances[ className ];
	}
	
	static remove( className ) {
		
		if ( !Singleton.instances || !Singleton.instances[ className ] ) return;
		Singleton.instances[ className ] = null;
	}
}

Sketch pad for Singleton implementations in ES6 JS

I still find this general pattern useful.