oop - JavaScript private methods

Question

To make a JavaScript class with a public method I'd do something like:

function Restaurant() {}

Restaurant.prototype.buy_food = function(){
   // something here
}

Restaurant.prototype.use_restroom = function(){
   // something here
}

That way users of my class can:

var restaurant = new Restaurant();
restaurant.buy_food();
restaurant.use_restroom();

How do I create a private method that can be called by the buy_food and use_restroom methods but not externally by users of the class?

In other words, I want my method implementation to be able to do:

Restaurant.prototype.use_restroom = function() {
   this.private_stuff();
}

But this shouldn't work:

var r = new Restaurant();
r.private_stuff();

How do I define private_stuff as a private method so both of these hold true?

I've read Doug Crockford's writeup a few times but it doesn't seem like "private" methods can be called by public methods and "privileged" methods can be called externally.

Answer 1

You can do it, but the downside is that it can't be part of the prototype:

function Restaurant() {
    var myPrivateVar;

    var private_stuff = function() {  // Only visible inside Restaurant()
        myPrivateVar = "I can set this here!";
    }

    this.use_restroom = function() {  // use_restroom is visible to all
        private_stuff();
    }

    this.buy_food = function() {   // buy_food is visible to all
        private_stuff();
    }
}