JSFiddle - React, Tailwind, and code Playground

JavaScript

var Client = (function() {
	// Our "private" instance
	var instance;
	
	// The constructor
	function Client() {
	
		// If it's being called again, throw an error
        if (typeof instance != "undefined") {
            throw new Error("Client can only be instantiated once.");
        }
	
		// initialize here
		
		// Keep a closured reference to the instance
		instance = this;
	}
	
	// Add public methods to Client.prototype
	Client.prototype.myPublic = function() {
		
	}
    
    Client.getSingletonInstance = function() {
        if (typeof instance == "undefined") {
            return new this();
        }
        else {
            return instance;
        }
    }
    
	// Return the constructor
	return Client;
})();


var NewObject = function () { 
    this.method1 = function() { }
};

var c1 = Client.getSingletonInstance();
var c2 = Client.getSingletonInstance();

console.log(c1 == c2); // true