Comments on: A common problem with the powerful javascript closures

By: Gilbert

Gilbert — Thu, 14 Jun 2007 11:46:19 +0000

function test(){
var i = 10;
var f = new Function(‘alert(‘ + i + ‘);’);
f();
}
test();

This works

By: Dan

Dan — Tue, 17 Apr 2007 17:57:31 +0000

Dammit! You’re right. Thanks!

By: BK

BK — Tue, 17 Apr 2007 17:46:38 +0000

this works if you put it global.
Now, try this:
function test(){
var i = 10;
var f = new Function(“alert(i);”);
f();
}
test();

Result: i is undefined in both FF and IE -> No Closure

By: Dan

Dan — Tue, 17 Apr 2007 17:41:51 +0000

BK, closures are everywhere! Even with Function… try that code.

var i = 10;
var f = new Function(“alert(i);”);
f();

Update : I am wrong! Look at the next comment from BK

By: BK

BK — Tue, 17 Apr 2007 16:50:54 +0000

I agree that they’re Evil to write and maintain but still the only way (I know) of creating a function in a function without closure and for an application that would need to run in a very limited memory space, you could have no choice (except maybe to create the function outside of the function)

By: Dan

Dan — Mon, 16 Apr 2007 22:44:51 +0000

@jsn : I didn’t redefine alertFunction, it’s just that I have alertFunction and alertFunctions (with a “s”).

@BK : Like Aaron said, Function is a bitch. It would be a big problem if the function would be just a bit more complex…

By: Aaron Faanes

Aaron Faanes — Mon, 16 Apr 2007 21:48:22 +0000

BK: While that would work, new Function is just a synonym for eval(), and uses of eval() are problematic at best since “complicated ‘string ” + concate + “‘ nation is a bitch to ” + write + (and * debug).

For that example, it’s probably not that important either way, since there’s little security, performance, or clarity issues at all with doing it any way, but I figured it’s worth mentioning my dislike for it in general.

jimbojw: That ends up using a closure itself anyway, hidden behind a method call.

Function.prototype.bindAsEventListener = function(/* some args */) {
var that = this;
var args = arguments;
return function() { return that.call.apply(that, args); }
}

I’m not saying it won’t work, I’m just saying that Prototype isn’t beyond closures.

By: BK

BK — Mon, 16 Apr 2007 14:43:58 +0000

Again, the use of the Function constructor also does the trick here:
alertFunction=new Function(“alert(‘Number is ” + iNumber + “);”);
alertFunctions.push(alertFunction);

By: jimbojw

jimbojw — Thu, 12 Apr 2007 21:16:57 +0000

If you have access to the Prototype library, the bindAsEventListener can method can help with this.

http://wiki.script.aculo.us/scriptaculous/show/Function.prototype.bindAsEventListener

alertFunctions.push(
(function() {
alert(this);
}).bindAsEventListener(iNumber)
);

By: jsn

jsn — Thu, 12 Apr 2007 21:07:08 +0000

no need to define alertFunction() multiple times.

function alertFunction(x) { return function() { alert(x) } }

for (var iNumber = 0; iNumber