Javascript revealing module pattern, public properties

Question

I\'m trying to get my head round the revealing module pattern in javascript. I\'m puzzled by two things about the following code snippet.

        var Child =         


        

Answer 1

This is slightly different solution, that doesn't require a getter/setter and preserves totalPoints as a property.

    var Child = function () {

        var _api;

        return _api = {

            addPoints: addPoints,
            points: 100
        };

        /* ----------- */

        function addPoints(points) {
            _api.points += points;
            return _api.points;
        };

    };

Answer 2

You're passing a number here:

return {
    points: totalPoints,
    addPoints: addPoints
};

This piece of code is no different from:

return {
    points: 100,
    addPoints: addPoints
};

You're passing the value; not a reference to totalPoints (the latter is not possible in JavaScript). So when totalPoints changes, the value in the object does not.

---

Using a function

The simplest way to get around this is to use a function to get the most up-to-date result (like getPoints which you already have). This JSFiddle gives a complete example:

return {
    points: function(x) { return totalPoints; }, // always up-to-date
    addPoints: addPoints
};

The downside is that the caller must now ask for points as a function call:

console.log(george.points());

---

Using a getters and setters

Another solution is using getters which would enable you to get an updated value with just george.totalPoints, though getters are not widely supported (yet). You could implement a getter like this:

var obj = {};

obj.points = addPoints;

// add a "special" property to the object instead of normal notation
Object.defineProperty(obj, "totalPoints", {
    get: function() { // function that's executed when you use `.totalPoints`
        return totalPoints;
    }
});

return obj;

---

Secondly, dropping var makes the functions global which is correct but not advisable. You could make one var statement using commas, if that's what you mean:

var totalPoints = 100, // expands to three `var` statements, so no
    addPoints = ...,   // global variables
    getPoints = ...;