Oops, this:
> Since the closure holds a
> reference to all of myNiftyMethods local variables and params (even
> though it doesn't use them), and since the object instance keeps a
> reference to the closure, 'param', 'v1', 'v2', and 'v3' all live on
> for as long as the closure does.
...should end with "as long as the object instance does, or until
this.thingy is cleared."
(Proofread, *then* post.)
-- T.J. ;-)
On Feb 23, 10:01 am, "T.J. Crowder" <[EMAIL PROTECTED]> wrote:
> Hi,
>
> > Closures is something that (can) cause memory leaks, right?
>
> That's a complex topic. :-) Closures inherit, and therefore preserve
> for their lifecycles, all of the local variables and parameters of the
> functions they're defined in. If the closure is used immediately and
> discarded, you don't much care. If you're going to retain a reference
> to the closure (for instance, an event handler, or a dynamically-
> created instance method), then you want to be aware of this. Here's
> an example of the latter case:
>
> function myNiftyMethod(param)
> {
> var v1, v2, v3;
>
> // ... do something ...
>
> // create and retain a closure to do something
> this.thingy = function() {
> // ... some code for the closure ...
> };
>
> }
>
> When myNiftyMethod is executed, it creates a closure and remembers it
> on the object instance as this.thingy. Since the closure holds a
> reference to all of myNiftyMethods local variables and params (even
> though it doesn't use them), and since the object instance keeps a
> reference to the closure, 'param', 'v1', 'v2', and 'v3' all live on
> for as long as the closure does. (Modulo cool JavaScript engine
> optimisations, which I don't think are common yet and are harder for
> the engine to do than it would at first seem.)
>
> So closures can have memory *implications*; if you understand how they
> work, though, and get used to some idioms around them, you won't cause
> memory leaks (barring JavaScript engine bugs).
>
> This is rambling a bit, but here's an example of the case where you're
> using the closure immediately and discarding it:
>
> function myNiftyMethod(someArray)
> {
> var v1, v2, v3;
>
> // ... do something ...
>
> // create and retain a closure to do something
> someArray.each(function(item) {
> item.doSomethingCool();
> });
>
> }
>
> You don't keep a reference to the closure used in the each() method,
> so you don't have to consider the implications of myNiftyMethod's
> parameters and variables being retained. And it's a very powerful and
> expressive way to deal with each item in the array.
>
> > - I'm getting lost in how you constructed the onSuccess callback...
>
> That's easy to do. :-) He's using a closure to construct and return
> another closure; it's the inner one that gets assigned to the
> onSuccess handler and retained, the outer one is run immediately and
> discarded. If you look carefully at the code defining the onSuccess
> handler, you'll see that the entire outer closure is wrapped in parens
> -- the opening paren is right after "onSuccess:", and then right at
> the end of the closure you see the closing paren followed by "(item)"
> -- that "(item)" tells you he's *executing* the outer closure right
> then, not just creating it. When it runs, the outer closure creates
> the inner closure and returns it. *That's* what gets assigned to
> onSuccess, the reference to the inner closure. The outer closure has
> only the param it needs (item) and no local variables, so the inner
> closure only preserves the information it really needs, not all of the
> local variables where all of this is running.
>
> Hope this helps,
> --
> T.J. Crowder
> tj /crowder software / com
>
> On Feb 23, 7:34 am, "Manu Temmerman-Uyttenbroeck"
>
> <[EMAIL PROTECTED]> wrote:
> > Hi,
>
> > Closures is something that (can) cause memory leaks, right?
> > kangax, would you mind explaining in a bit more detail why you wrote the
> > code like you wrote it? I'm a bit lost in it. I restructured the code you
> > wrote a bit...http://pastie.caboo.se/156248
> > - Is there a reason why you don't write a ';' after the new Ajax.Request
> > (...)?
> > - Is there a reason why you don't write a ';' after the
> > someArray.each(function(item)
> > { ... })?
> > - I'm getting lost in how you constructed the onSuccess callback...
>
> > Thx...
>
> > Manu.
>
> > On Fri, Feb 22, 2008 at 11:11 PM, kangax <[EMAIL PROTECTED]> wrote:
>
> > > Looks like a closure issue to me (solved with another closure).
> > > Also, is that an array you are iterating over using "for..in" ?
>
> > > siteListArray.each(function(item) {
> > > var url = 'functions.php?command=numberOfErrors&site=' + item;
> > > new Ajax.Request(url, {
> > > onSuccess: (function(item) { return function(t) {
> > > $('sidebar_site_div_' + item).update(t.responseText);
> > > }})(item)
> > > })
> > > })
>
> > > - kangax
>
> > > On Feb 22, 4:02 pm, Chach <[EMAIL PROTECTED]> wrote:
> > > > Hi everybody,
>
> > > > I'm just getting kicked off on prototype and I'm having a problem that
> > > > I'm hoping to get some help on.. I've had good success with
> > > > Ajax.Updater, but now I'm trying to use Ajax.Request with the use of
> > > > its callback abilities. My issue is that I'm trying to get a hold of
> > > > one of the Element objects in the DOM using $('element'), however the
> > > > name of the element can vary and so I have to assemble the name using
> > > > the value in an array. It's almost like the siteListArray[x] does not
> > > > work in the callback. Is it possible that the callback cannot see a
> > > > variable that was declared earlier in my code at a global scope?
> > > > Thanks in advance.
>
> > > > for (x in siteListArray)
> > > > {
> > > > var url = 'functions.php?command=numberOfErrors&site=' +
> > > > siteListArray[x];
> > > > new Ajax.Request(url, {
> > > > asynchronous:true,
> > > > onComplete: function(transport) {
> > > > $('sidebar_site_div_' +
> > > > siteListArray[x]).update(transport.responseText);
> > > > }
> > > > });
>
> > > > }
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