JavaScript: Passing parameters in to an indirect, anonymous function

Question

I want to implement data hiding in JavaScript by writing a function that returns an object from inside a closure. Here is the incorrect code:

pokerObjects.getPokerCard = (function(f, s){
        // These are immutable, so hide them in the closure
        var face = (typeof f === 'number' ? pokerObjects.faces[f] :  f);
        var suit = (typeof s === 'number' ? pokerObjects.suits[s] :  s);

        return {
            to_s: function() { return face + " of " + suit; }
          };

      })(f,s);

What I would like to do is be able to call the function getPokerCard with two parameters and have those parameters passed to the anonymous function defined parenthetically. But, passing them as written above gives me a ReferenceError: f is not defined when I try to parse the code.

Why do they "need to be passed"? Your question is a little unclear. — Pointy
– Pointy, Commented Dec 7, 2011 at 15:08
Explain where the parans f,s that you are passing to the anon function where they come from, and why can't you check face and suit every time, is this an final property or a method? It's unclear... — Gabriel Gartz
– Gabriel Gartz, Commented Dec 7, 2011 at 15:17

Phil Klein · Accepted Answer · 2011-12-07 15:14:14Z

2

Maybe I'm not understanding your question correctly, but it seems like you want to assign a function to pokerObjects.getPokerCard which would allow you to later call pokerObjects.getPokerCard(f, s) which returns the object with getFace, getSuit, and to_s.

pokerObjects.getPokerCard = function(f, s) {
    // These are immutable, so hide them in the function.
    var face = (typeof f === 'number' ? pokerObjects.faces[f] :  f);
    var suit = (typeof s === 'number' ? pokerObjects.suits[s] :  s);

    return {
        getFace: function() { return face; },
        getSuit: function() { return suit; },
        to_s: function() { return face + " of " + suit; }
    };
};

This accomplishes the same thing, while still ensuring that face and suit remain hidden. They are scoped variables within the function.

answered Dec 7, 2011 at 15:14

Phil Klein

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1 Comment

Raynos Over a year ago

This "data hiding" doesn't hide any data and comes at significant run-time penalty. Practices like these should be avoided.

Raynos · Accepted Answer · 2011-12-07 15:21:17Z

0

pokerObjects.getPokerCard = getPokerCard;

Card.prototype.toString = cardToString;

function getPokerCard(face, suit) {
  return new Card(
    typeof face === "number" ? this.faces[face] : face, 
    typeof suit === "number" ? this.suits[suit] : suit
  );
}

function Card(face, suit) {
  this.face = face;
  this.suit = suit;
}

function cardToString() {
  return this.face + " of " + this.suit;
}

There is no private in JavaScript. There is no point in data hiding if you expose getters for the data. Just use properties instead (make then non-writable if you really want)

edited Dec 7, 2011 at 15:21

answered Dec 7, 2011 at 15:11

Raynos

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2 Comments

Yes - that Jake. Over a year ago

This doesn't allow the data-hiding, which was the point of the original exercise. face and suit are properties of the card object, but should be defined inside the closure instead.

Raynos Over a year ago

@Jekke why do you want data hiding, again you expose getters for it, so your not hiding anything. As an aside you can't have "data hiding" without severe run-time penalties, so avoid it

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