IsDefined()? 1

[mattquantic]

Hi, I would like to pass a parameter to an included function, but not have to update all of my scripts that call it.

Is there an IsDefined function? I was going to count the arguments, but that is not that future proof...

M@)

 

[BabyJeffy]

I use the following to test:

if (typeof variableName == "undefined")

Jeff

 

[mattquantic]

Ace! - cheers... M@)

 

[theboyhope]

Deciding to have a shot at writing an actual isDefined() function — wish I hadn't bothered now. ;-)

Any of you guys (you know who you are) got a solution for the scope problem demo'd below?

function isDefined( checkVar ) {

	return ( typeof window[ checkVar ] == "undefined" ? false : true );
}

alert( "window defined? " + isDefined( "window" ) );
alert( "nothing defined? " + isDefined( "nothing" ) );

function test() {

	var monkey = 1;
}

alert( "monkey defined? " + isDefined( "monkey" ) );

Is that the most counter-intuitive if() statement ever or what. Heheh.

 

[theboyhope]

PS - eval() is cheating. ;-)

 

[BillyRayPreachersSon]

>> Any of you guys got a solution for the scope problem demo'd below?

What scope problem? Are you talking about monkey being undefined? If you are, why is that a scope problem - monkey is a local variable, and so shouldn't be available globally.

Dan

 

[theboyhope]

Precisely. How to check if non-blobal variables are defined ...

 

[theboyhope]

Heh - global, even.

 

[BillyRayPreachersSon]

Well - you would just use Jeff's test within the scope of the local variable, surely?

Testing anything outside its scope would always be fruitless, surely? ;o)

Dan

 

[theboyhope]

Yeah, of course the standard version still works.

Testing anything outside its scope would always be fruitless, surely?

Yeah, but that's not what would be happening is it. Think about it.


I don't think it's gonna work with functions anyways — certainly can't think of a way. But hey! - that's why I asked, right. ;-)

 

[boelem]

Mattquantic,

I'm never fond of creating globals when you actually want to pass a parameter.

You could add a new parameter to an existing function:

f(a,b) {...} becomes f(a,b,c) {...}

where inside f you can test on passing c:

function f(a,b,c) {
c = (c ? c : defaultValueFor_c)
...
}

or

function f(a,b,c) {
if(c) { ... code when passing c ... }
...
}

Hope that helps,

Boelem