var test = function(){
  return {
    name: 'lluis',
    age: 30
  }
}

var obj = test();

console.log(obj); //prints { name: 'lluis', age: 30 }

obj.name = 'Alessio';
obj.age = 36;
obj.country = 'Italy';

var str = 'Obj ' + JSON.stringify(obj);
console.log(str); //prints Obj {"name":"Alessio","age":36,"country":"Italy"}