function pointers vs direct calling in javascript

[Sampat]

Hi,
I wanted to know the performance of calling a function pointer v/s a
normal function call in javascript in a scenario where there are
multiple calls in the js to the same function. Please share your
thoughts if someone has worked on this.

Thanks,
Sampat.

[getsanjay.sharma]

On Nov 22, 12:46 pm, Randy Webb <HikksNotAtH... @aol.comwrote:

A case where I wouldn't want it to go outside looking for it?

var tempVar = new Array();
//lots of entries in tempVar here

function something(){
tempVar = "...."

}

function somethingElse() {
alert('hey, where did my array go?')
}

Agreed. That is one of the reasons why I prefix globals with g_ and so
called constants with c_ .

A case where I would? The altering of a global variable, an array, or
several other things.

var myArray = new Array();

Give it some thought :)

Huh? I am confused.

It isn't that simple though.

var someVar = "global variable";
function someFunction(){
var someVar = "local variable";
someVar = "modified in the function";
alert(window['someVar'])
}

Without testing, what will the alert say, and why? Then test it and see
if you were right without testing it :)

I was able to guess the output without running it. The answer would be
'global variable' because AFAIK javascript starts searching for an
identifier from the closest scope to the most generic scope.

But then again, I might be wrong so please feel free to correct me. :-)

[Randy Webb]

ge************* *@gmail.com said the following on 11/22/2007 11:38 AM:

On Nov 22, 12:46 pm, Randy Webb <HikksNotAtH... @aol.comwrote:

>A case where I wouldn't want it to go outside looking for it?

var tempVar = new Array();
//lots of entries in tempVar here

function something(){
tempVar = "...."

}

function somethingElse() {
alert('hey, where did my array go?')
}

Agreed. That is one of the reasons why I prefix globals with g_ and so
called constants with c_ .

l_ for local might be a better prefix.

<snip>

The answer would be 'global variable' because AFAIK javascript
starts searching for an identifier from the closest scope to the
most generic scope.

When looking it up, yes. When assigning to it, no. The use of the 'var'
keyword stops it from going "up" the scope chain.

I think there is an old thread somewhere where Richard Cornford
explained it better than I have. I just can't find it right now.
Searching the Google archives for "var" is, well, kinda pointless :)

--
Randy
Chance Favors The Prepared Mind
comp.lang.javas cript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[RobG]

On Nov 23, 11:46 am, Randy Webb <HikksNotAtH... @aol.comwrote:
[...]

When looking it up, yes. When assigning to it, no. The use of the 'var'
keyword stops it from going "up" the scope chain.

I think there is an old thread somewhere where Richard Cornford
explained it better than I have.

Here's one that includes - with -:

<URL:
http://groups.google.com.au/group/co...4a50b8acebecd5

>

--
Rob

[Thomas 'PointedEars' Lahn]

obG wrote:

On Nov 22, 4:37 pm, getsanjay.sha.. [e-mail] wrote:

>You don't need 'var' keyword to *declare* variables

Yes, you do. A variable without var isn't declared, it is created as
a property of the global object when the code executes. It is
equivalent (more or less) to:

window[variableName] = 'foo';

(Sigh. [psf 10.1] More or less; rather less. It should be

window['variableName'] = 'foo';

if that; `window' does not need to refer to the Global Object.)

IOW, a variable that is not declared with `var' is not a variable at all.
The identifier will refer to a property of an object O in the Scope Chain.
O is often the Global Object, which should be at the end of the Scope Chain,
but O does not need to. During identifier resolution, the first object that
reports to have such a property will be O.

In fact, O may be not a host object which makes this initialization-only
approach error-prone. It is known that in the MSHTML DOM IDs and names of
markup elements make up property names of an host object that is before the
Global Object in the Scope Chain which is why you get a runtime error if you
try write access to those properties.)

(Maybe I should create a template for that as people keep forgetting it even
though I post the reminder frequently.)
PointedEars

[getsanjay.sharma]

Thanks a lot Randy, Rob and Thomas for your enlightening. It would
take some time for all that to seep inside but when in doubt I know
where to turn to. :-)

Thanks and regards,
/~STS

[Thomas 'PointedEars' Lahn]

Thomas 'PointedEars' Lahn wrote:

IOW, a variable that is not declared with `var' is not a variable at all.
The identifier will refer to a property of an object O in the Scope Chain.
O is often the Global Object, which should be at the end of the Scope Chain,
but O does not need to. During identifier resolution, the first object that
reports to have such a property will be O.

In fact, O may be not a host object which makes this initialization-only
approach error-prone. [...]

That should have either been "may not be a _native_ object" or "_may be_ a
host object_", of course. Sorry for causing confusion.
PointedEars