Question

I saw this pattern:

Money = (function() {
    function Money(rawString) {
        this.cents = this.parseCents(rawString);
    }
});

in this CoffeeScript screencast preview. (The homepage for the screencast is here.)

Now, I don’t understand this pattern. There is a Money function that contains a Money function. What’s that about?

Could someone explain?

Answer 1

As quoted, there’s no point to that pattern other than that the outer Money symbol can be deleted from the window object (except on IE7 and below, but that’s another story) because it’s a normal (implicit) property of window (as opposed to a var or a symbol deriving from a function declaration). But even then, the outer Money symbol receives a function that does absolutely nothing. Could it be misquoted?

For instance, here’s a fairly standard patttern:

Money = (function() {
    var someCompletelyPrivateVariable;

    function doSomethingCompletelyPrivate() {
    }

    function Money(rawString) {
        this.cents = this.parseCents(rawString);
    }

    return Money;
})();

That’s the module pattern, and it lets you have completely private variables and functions (both illustrated) whilst only having one public symbol. But I’ve had to edit a fair bit to create that (the most significant edits being the return Money; at the end and the addition of () after the anonymous function so we’re calling it rather than just defining it.