singleton.js

var singleton = (function () {
  var instance;
 
  function init() {
    function privateMethod(){
      console.log( "I am private" );
    }
 
    var privateVariable = "I am a private variable";
    var privateRandomNumber = Math.random();
 
    return {
      publicMethod: function () {
        console.log( "I am a public method" );
      },
      publicProperty: "I am a public property",
      getRandomNumber: function() {
        return privateRandomNumber;
      }
    };
  };
 
  return {
    getInstance: function () {
      if ( !instance ) {
        instance = init();
      }
      return instance;
    }
  };
})();