How to make a singleton in javascript

gistfile1.js

function MySingletonObject() {
  // SINGLETON CONSTRUCTOR
	if (MySingletonObject.prototype._singletonInstance) {
		return MySingletonObject.prototype._singletonInstance;
	}
	MySingletonObject.prototype._singletonInstance = this;
	//
  
  // OBJECT PROPERTIES
  this.PublicProperty = 42;
  var PrivateProperty = "foo";
  //
  
  // OBJECT METHODS
  this.PublicMethod = function () {
    return true;
  }
  var PrivateMethod = function () {
    return "bar"
  }
  //
}
// USAGE
var mso = new MySingletonObject();