Comments on: Limiting Variable Scope Using (function(){})();

By: antonio torres

antonio torres — Mon, 14 Dec 2009 19:18:44 +0000

hi David!

i hope you can help me.
is it possible to implement your “load more posts” widget (http://net.tutsplus.com/tutorials/javascript-ajax/create-a-twitter-like-load-more-widget/) on a blogger blog? i guess the problem is the php implementation..
i like very much the script but i supose is not possible to implement it on a blogger thing…

any idea on that, David? maybe a go around trick…
thank you very much in advance
antónio torres
http://www.vaiumagasosa.com

By: Jeremy Martin

Jeremy Martin — Mon, 14 Dec 2009 16:47:48 +0000

Good post. Function scoping is a great way to keep your code clean. I often use a model like this:

(function() {
// all my private stuff (vars and funcs) go here
var foo = ‘I am scoped, no one else sees me’;

var apiMethods = {
// publicly exposed methods here
// these methods still have access to privately scoped members
bar : function() { alert(foo); }
};

// expose api methods
window.MyNameSpace = apiMethods;
})();

// alerts value of foo
MyNameSpace.bar();

By: David Walsh

David Walsh — Mon, 14 Dec 2009 15:17:01 +0000

Ugh, updated my post as the terminology was off. This should make more sense and be more direct.

By: TheBigBabou

TheBigBabou — Mon, 14 Dec 2009 15:09:52 +0000

Sorry David, I don’t want to be offensive, but your code examples are no closures. What you are showing and describing is limiting variables to function scope.

A closure is a function or codepointer which accesses variables outside its scope. Like here:

(function () {

var out = 1;

window.setTimeout(function () {
alert(out);
}, 100);

})()

The closure here would be the function, which is the first parameter to setTimeout. It doesn’t declare a variable “out”, but is able to access “out” from its outer function scope. As long as a variable stores a reference to this function, “out” is not freed from memory as well.

By: Will

Will — Mon, 14 Dec 2009 15:03:41 +0000

Doesn’t this sort of miss the point of closures? I always thought that ‘closure’ meant it ‘closed’ over variables available to it when being declared, so those variables were available even when they went out of scope. It’s hard to explain, but this example might help:

function makeClosure() {
var t = “foo”;
return function() {
alert(t + “bar”);
}
}

So, you’d call makeClosure, which would return a function. Whenever the returned function was called, the value of t (“foo”) would still be available to it (thus returning “foobar”) even though t’s scope had expired when makeClosure ended.

By: David Walsh

David Walsh — Mon, 14 Dec 2009 14:31:55 +0000

In this case you could define $$(‘a’) globally but my example was more trying to display the two closures working separately.

By: Richard

Richard — Mon, 14 Dec 2009 14:29:23 +0000

Proper programming technique is to define variables before use, and to use as few (preferably no) global variables as possible. What you have done in the examples are a work-around.

I love all your other articles though!