What is wrong with my singleton design pattern?

Question

 var singleton = (function(){

  var instance;

  function init(){

  var privateVariable = 'Private'
  var privateMethod   = function(){ console.log('Am private');}

    return {

    publicField  : 'Public',
    publicMethod : function(){ console.log('Am public');},
    randomVar    : Math.random()
  };
};

return function(){
  if(!instance) { instance = init(); } 
  else { return instance; }
}

})();

var single1 = singleton();
var single2 = singleton();

console.log(single1.randomVar == single2.randomVar);

Should return true ,returned: TypeError: single1 is undefined, But if i removed the IIFE wrap around the function, it works perfectly so i didn't get why is that?

Answer 1

On the initial call you are not returning anything, you are just initializing it - hence the undefined. Putting a return instance after the initialization call should do the trick.

Answer 2

I guess you wanted this. Always return instance, even the first time

return function(){
   if(!instance) {
      instance = init();
   } 
   return instance;
}

Answer 3

You either want to add a return keyword

return function(){
  if(!instance) { return instance = init(); } 
  else { return instance; }
}

or omit the else:

return function(){
  if(!instance) { instance = init(); } 
  return instance;
}

Answer 4

Remove else part in your return.

  return function() {
    if (!instance) {
      instance = init();
    }
    return instance;
  }

var singleton = (function() {

  var instance;

  function init() {

    var privateVariable = 'Private'
    var privateMethod = function() {
      console.log('Am private');
    }

    return {

      publicField: 'Public',
      publicMethod: function() {
        console.log('Am public');
      },
      randomVar: Math.random()
    };
  };

  return function() {
    if (!instance) {
      instance = init();
    }
    return instance;
  }

})();

var single1 = singleton();
var single2 = singleton();

console.log(single1.randomVar == single2.randomVar);