Lifetime of a functions private variables

#1

I have a question regarding the lifetime of a functions private variables.

From my knowledge in other languages I would expect a functions private
variables to be "unreachable" as soon as the function has finished executing
(which in some other languages would pop off the variables from the stack)
but it looks to me that javascript is working somewhat different.

The following code shows that the private variable "i" can be reached by the
both interval-functions after the functions scope is left - why is that ?

Is this a "dirty" way to address the variable or is it fully supported ?

function c() {
document.forms.myform.text1.value = "";
document.forms.myform.text2.value = "";
var i = 0;
var timer1 = window.setInterval(
function() {
document.forms.myform.text1.value = i;
}, 500, "javascript" );
var timer2 = window.setInterval(
function() {
document.forms.myform.text2.value = i++;
}, 1000, "javascript" );
}

<body onload="c();">
<form name="myform" action="">
<input type="text" name="text1" size="50" />
<br />
<input type="text" name="text2" size="50" />
</form>
</body>

Best regards
Johnny Nielsen

#2

Johnny Nielsen wrote:

Quote:

I have a question regarding the lifetime of a functions private variables.

From my knowledge in other languages I would expect a functions private
variables to be "unreachable" as soon as the function has finished executing
(which in some other languages would pop off the variables from the stack)
but it looks to me that javascript is working somewhat different.

The following code shows that the private variable "i" can be reached by the
both interval-functions after the functions scope is left - why is that ?

Is this a "dirty" way to address the variable or is it fully supported ?
snip

Formalised in ECMA 262, 3rd Ed. and also supported (more or less) in
some preceding browser. See:-

<URL: http://jibbering.com/faq/faq_notes/closures.html >

Richard.

#3

Thanks. From my understanding it looks like these "closures" is something
one should really be aware of when dealing with Ajax/webservice-based
"static" pages where memory usage might build up.

Best regards
Johnny Nielsen

"Richard Cornford" <Richard (AT) litotes (DOT) demon.co.uk> wrote

Quote:

Johnny Nielsen wrote:
I have a question regarding the lifetime of a functions private
variables.

From my knowledge in other languages I would expect a functions private
variables to be "unreachable" as soon as the function has finished
executing
(which in some other languages would pop off the variables from the
stack)
but it looks to me that javascript is working somewhat different.

The following code shows that the private variable "i" can be reached by
the
both interval-functions after the functions scope is left - why is that ?

Is this a "dirty" way to address the variable or is it fully supported ?
snip

Formalised in ECMA 262, 3rd Ed. and also supported (more or less) in
some preceding browser. See:-

URL: http://jibbering.com/faq/faq_notes/closures.html

Richard.

#4

Johnny Nielsen wrote:

Quote:

From my understanding it looks like these "closures" is something
one should really be aware of when dealing with Ajax/webservice-based
"static" pages where memory usage might build up.

Closures are a consequence of the fundamental nature of javascript.
Nobody can reasonably clam to understand javascript without
understanding closures, when and how to use them and when and why not
to. My opinion would be that nobody should even consider touching an
area as issue-heavy as AJAX/web-services without first acquiring a
complete understanding of javascript.

Richard.

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Lifetime of a functions private variables

JavaScript discussion (multi-lingual) JavaScript discussion (alt.comp.lang.javascript)

Lifetime of a functions private variables - 05-01-2006 , 06:40 PM

Re: Lifetime of a functions private variables - 05-02-2006 , 06:53 AM

Re: Lifetime of a functions private variables - 05-04-2006 , 12:56 PM

Re: Lifetime of a functions private variables - 05-07-2006 , 11:27 AM