Edit in JSFiddle

//http://www.jermywells.com

"use strict";
var Singleton = function () {
    //if (Singleton.prototype.instance) {
    //    return Singleton.prototype.instance;
    //}
    //Singleton.prototype.instance = this;
    
    var instanceName = "";
    this.setInstanceName = function (n) {
        instanceName = n;
    };
    this.getInstanceName = function () {
        return instanceName;
    };
};

var firstSingleton = new Singleton();
firstSingleton.setInstanceName('first One');

var secondSingleton = new Singleton();
secondSingleton.setInstanceName('second One');

document.getElementById('first').innerHTML = firstSingleton.getInstanceName();
document.getElementById('second').innerHTML = secondSingleton.getInstanceName();

<div id="first"></div>
<div id="second"></div>