If you use non EcmaScript6 JS version (which currently ruin in most browsers), you can do it like this:

function Human() {
    var agePrivate = 0;
    var self = {
        agePublic: 0,
        setAge: function ( a )  {
            agePrivate = a;
            self.agePublic = a + 1;
        },
        getAge: function ( )  {
           return agePrivate;
        },
   } 
   return self;
}

h = Human();  // create object
h.setAge(10); // call setter
console.log("getter:", h.getAge()) // use getter 
console.log("public:", h.agePublic) // use public field
console.log("private:", h.agePrivate) // will return undefined - you can't access to private field

Private methods can be implemented in same way

#javascript