Where do function variables live?

**Random** · Jul 23 '05, 07:58 PM

Re: Where do function variables live?

I'm not sure how to do exactly what you're trying here, or even if it
can be done. I'll hope someone posts a more appropriate response.

Assuming it can't, here's what I'd try:

function sample( obj ) {
var key1 = obj.key1 || null;
var key2 = obj.key2 || null;

key1 && alert( 'key1 = ' + key1 );
key2 && alert( 'key2 = ' + key2 );
}

Or you might try something like this:

function sample( arOptions ) {
var arVars = new Array();

for( idx in arOptions )
arVars[ idx ] = arOptions[ idx ];

alert( 'key1 = ' + arVars[ 'key1' ] );
}

Or you might look into making your own object, if it suits your needs
here.

I can't make any better recommendations without understanding more of
your end goal.

VK · Jul 23 '05, 07:58 PM

Re: Where do function variables live?

You cannot treat literals (var name) as a strings, no way. You can
regenerate your function body though:

<html>
<head>
<title>Untitl ed Document</title>
<meta http-equiv="Content-Type" content="text/html;
charset=iso-8859-1">
<script>
var dynFun = null;
function dynFunMaker(k, v) {
dynFun = new Function('var '+k+'=\''+v+'\' ;alert('+k+');' );
dynFun();
}
</script>
</head>

<body bgcolor="#FFFFF F" onload="dynFunM aker('myVar','O K')">
</body>
</html>

VK · Jul 23 '05, 07:58 PM

Re: Where do function variables live?

....and if study someone's function, you can get dump the function code
to string:

var funText = functionName.ar guments.callee || functionName;

and study the text using indexOf() or regular expressions.

**Csaba Gabor** · Jul 23 '05, 07:58 PM

Re: Where do function variables live?

Csaba Gabor wrote:[color=blue]
> for example, I'd like to call
> function sample(oOptions ) {
> var key1 = "key1 default";
> var key2 = "key2 default";
> var idx;
> if (arguments.leng th>0)
> for (idx in oOptions)
> window.sample[idx] = oOptions[idx]; // this line wrong
>
> alert (key1);
> }[/color]
[color=blue]
> with sample({key1:"k ey1 was set"}) and have the alert be:
> "key1 was set"[/color]

Subsequently, Random wrote:[color=blue]
> I'm not sure how to do exactly what you're trying here, or even if it
> can be done. I'll hope someone posts a more appropriate response.[/color]

....[color=blue]
> I can't make any better recommendations without understanding more of
> your end goal.[/color]

My goal is just to understand the DOM better as it relates to functions
and their variables. The background motivation was in thinking about a
compact way to provide named arguments to javascript functions (which
is useful if you have a large universe of possible options that you
aren't expecting to change from default values). The following slight
modification does what I want (though not bulletproof - nothing ensures
that all the variables passed in will be local unless I've already
declared them inside the function with var), but it uses the much
reviled eval:

function sample(oOptions ) {
var key1 = "key1 default";
var key2 = "key2 default";
var idx;
if (arguments.leng th>0)
for (idx in oOptions)
eval(idx + " = oOptions[idx]"); // <= eval usage

alert (key1);
alert (key2);
}

sample({key1:"k ey1 was set"});

The point is that this is a small piece of portable code which could be
plunked into any function (just make sure it comes after defaults are
set). There is no need for customization of the code dealing with
oOptions on a per function basis. It's up to the caller to pass in
whatever it would like to override. Still, It would be nice if that
eval weren't there ...

Csaba Gabor from Vienna

VK · Jul 23 '05, 07:58 PM

Re: Where do function variables live?

> The background motivation was in thinking about a ...

Well, you can use the fact that any object (including Function) extends
Object. So you can use Object's hash mechanics in your function:

function myFunction(k, v) {
myFunction.k = v;
// or delete(myFuncti on.k);
}

IMHO it's still rather pointless: now you have a new pseudo-var in your
function, but you have no way to notify function methods what literal
(var name) to use. You need to regenerate the entire function body (say
using new Function() method, see my prev posting).

**Michael Winter** · Jul 23 '05, 07:58 PM

Re: Where do function variables live?

On 23/05/2005 02:06, Csaba Gabor wrote:

[Subject:] Where do function variables live?

Local variables are properties of a variable/activation object owned by
every function object. However, this variable object is just a
specification mechanism: it's described by the specification for
expository purposes only, and is not something you can access in code.
[color=blue]
> I'd like to be able to pass a key1/value1 pair into a function and have
> that function have a local variable by the name of key1 to which value1
> is assigned.[/color]

An alternative to an actual local variable is along the lines of what
Random posted, only using an Object instance, rather than an Array instance.

function sample(pairs) {
var hash = {key1 : 'key1 default',
key2 : 'key2 default'},
key;

if(pairs) {
for(key in pairs) {
hash[key] = pairs[key];
}
}
alert(hash['key1']);
for(key in hash) {
alert(key + '\n' + hash[key]);
}
}

The object, hash, is obviously not a real hash table (see previous,
recent debates for reasons and solutions), but it may suffice. It is
also like any other local; it will be destroyed (usually) once execution
returns from the function. You could either make it (public) static by
creating it as a property of the function (similar to what you've done
already), or private static using a closure of some form:

var sample = (function() {
var hash = {key1 : 'key1 default',
key2 : 'key2 default'};

return function(pairs) {
var key;

if(pairs) {
for(key in pairs) {
hash[key] = pairs[key];
}
}
alert(hash['key1']);
for(key in hash) {
alert(key + '\n' + hash[key]);
}
};
})();

The outer function could obviously be an object constructor function if
sample was meant to be a method.

[snip]
[color=blue]
> window.sample[idx] = oOptions[idx]; // this line wrong[/color]

sample[idx] = oOptions[idx];

would be achieve the same thing. Going through the global object is
unnecessary.

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

Where do function variables live?

Where do function variables live?

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