Edit in JSFiddle

//http://www.jermywells.com
//js singleton

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

    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>