Hi,
> The author of coffeescript mentioned on this thread (http://github.com/
> jashkenas/coffee-script/issues/issue/675/#issue/675/comment/402197)
> that ie leaks memory if you use named functions, instead of closures.
IE doesn't leak memory if you use named functions (or at least, I've
never heard of it doing so). I'm pretty sure jashkenas was talking
about a bug IE has related to named function *expressions*, which are
a different thing. Prototype doesn't use any named function
expressions.
Here's a named function declaration:
function foo () {
}
Here's a named function *expression*:
var f = function foo() {
};
The difference being that you're using the function as a right-hand
value in an expression. (A right-hand value is the value to the right
of an = in an assignment, to the right of a : in a property
initializer, or that you pass into a function when calling it.)
The short version of the bug is that IE will create two near-identical
functions instead of one if you use a named function expression. This
is wrong, and of course it means that IE uses double the memory it
should have, but it isn't a memory "leak" in the sense of ever-
increasing memory usage. Another aspect of the bug is that the symbol
`foo` gets defined in the containing scope, which is incorrect.
For more details, it happens that I just recently wrote this up
(although the bug has been around forever):
http://blog.niftysnippets.org/2010/09/double-take.html
IE isn't the only browser that has (or has had) issues with named
function expressions. kangax wrote up a very useful article a while
back on what NFEs are and how they get treated by various versions of
various JavaScript engines. The article is a couple of years old now
and the most recent implementations of many engines do better, though
not IE's JScript:
http://kangax.github.com/nfe/
Slightly off-topic, but you said "...named functions, instead of
closures...". Named functions *are* closures. Whether the function
has a name doesn't affect whether it closes over data. More about
closures here:
http://blog.niftysnippets.org/2008/02/closures-are-not-complicated.html
HTH,
--
T.J. Crowder
Independent Software Engineer
tj / crowder software / com
www / crowder software / com
On Sep 27, 3:01 am, Daniel Ribeiro <[email protected]> wrote:
> The author of coffeescript mentioned on this thread (http://github.com/
> jashkenas/coffee-script/issues/issue/675/#issue/675/comment/402197)
> that ie leaks memory if you use named functions, instead of closures.
> If this is true, why does Prototype uses some of these (such as
> function $A onhttp://prototypejs.org/assets/2009/8/31/prototype.js)?
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