JavaScript singleton implementation

javascript-singleton.js

/*
 * The instance symbol should be defined in the scope 
 * in which you want the singleton to exist. This does 
 * not necessarily mean globally. Just within your 
 * outermost execution context.
 */
let instance;

const Singleton = (() => {
    const createInstance = () => {
        const ts = String(new Date().getTime());
        console.log('Calling createInstance', ts)
        return `Instance timestamp : ${ts}`
    };

    return {
        getInstance: () => {
            if (instance === undefined) {
                instance = createInstance();
            }
            return instance;
        },
    };
})();

// This part just tests the above to verify it is a true singleton.
let counter = 0;
let tid = setInterval(() => {
  console.log( Singleton.getInstance() )
  counter++
  if (counter > 5) clearInterval(tid)
}, 1000);