Is it possible to initialize function parameters in Javascript?

**Robert** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

In article <40a31071$0$202 $75868355@news. frii.net>,
Hiroshi Ochi <hiroshi_ochi@n ospam.com> wrote:
[color=blue]
> Hello,
>
> Is it possible to initialize javascript function parameters (using MSIE
> 6.0 and above)? According to the link below, it seems possible to do
> this.
>
> http://www.mozilla.org/js/language/j...ale/named.html
>[/color]

You'll note that this is a JavaScript 2.0 reference. I believe that IE
6.0 implements Javascript 1.5

Robert

**Hiroshi Ochi** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

Hi Robert,

Hmm, too bad. I think I'll just do the below workaround:


<html>
<script language="javas cript">
function myFunc(paramOne ,paramTwo){
if(paramTwo == undefined)
paramTwo = someValue; // initialize default value
...
}
</script>
</html>


thanks,
hiroshi

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**Saint Jude** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

Hiroshi Ochi <hiroshi_ochi@n ospam.com> wrote in message news:<40a42507$ 0$202$75868355@ news.frii.net>. ..[color=blue]
> Hi Robert,
>
> Hmm, too bad. I think I'll just do the below workaround:
>
> 
> <html>
> <script language="javas cript">
> function myFunc(paramOne ,paramTwo){
> if(paramTwo == undefined)
> paramTwo = someValue; // initialize default value
> ...
> }
> </script>
> </html>
> [/color]

Comparing against undefined *may* be risky, and involve backward
compatibility problems. I'd go for: if(!paramTwo) - for an undefined
parameter test.

In fact JS has a good shortcut for your purpose:

if(paramTwo == undefined)
paramTwo = someValue; // initialize default value

becomes

paramTwo = paramTwo || someValue

**Lee** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

Saint Jude said:
[color=blue]
>Comparing against undefined *may* be risky, and involve backward
>compatibilit y problems. I'd go for: if(!paramTwo) - for an undefined
>parameter test.
>
>In fact JS has a good shortcut for your purpose:
>
> if(paramTwo == undefined)
> paramTwo = someValue; // initialize default value
>
>becomes
>
> paramTwo = paramTwo || someValue[/color]

I doubt that undefined would be a problem with any
implementation of Javascript. On the other hand,
both of your methods assume that zero, false, and
"" are not valid parameter values.

**Richard Cornford** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

Lee wrote:[color=blue]
> Saint Jude said:[color=green]
>>Comparing against undefined *may* be risky, and involve backward
>>compatibili ty problems. I'd go for: if(!paramTwo) - for an undefined
>>parameter test.
>>
>>In fact JS has a good shortcut for your purpose:
>>
>> if(paramTwo == undefined)
>> paramTwo = someValue; // initialize default value
>>
>>becomes
>>
>> paramTwo = paramTwo || someValue[/color]
>
>
> I doubt that undefined would be a problem with any
> implementation of Javascript. On the other hand,
> both of your methods assume that zero, false, and
> "" are not valid parameter values.[/color]

IE 4 doesn't like it; it produces the extremely helpful error message
"undefined is undefined." :)

But there is no need to risk the problem as - undefined - can be
implemented in unsupporting environments with:-

this.undefined = this.undefined;

-or:-

window.undefine d = window.undefine d;

- executed as inline code as the page loads.

Recent discussion on the identity operator - === - suggest that it has
probably moved into the set of more recent javascript features that can
now universally be relied upon as both Netscape 4 and IE 4 understand it
and they are the generation of browsers apparently now dropping out of
use. The identity operator doesn't type convert so identity comparison
with a normalised - undefined - should give an unambiguous result:

if(paramTwo === undefined){
... //paramTwo needs defaulting
}

- on current browsers without the risk of errors. But a - typeof - test
(if slower) should also produce a reliable result:-

if(typeof paramTwo == "undefined" ){
... //paramTwo needs defaulting
}

- without any real language version concerns as typeof has been around
since JavaScript 1.1.

Richard.

**Grant Wagner** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

Lee wrote:
[color=blue]
> Saint Jude said:
>[color=green]
> >Comparing against undefined *may* be risky, and involve backward
> >compatibilit y problems. I'd go for: if(!paramTwo) - for an undefined
> >parameter test.
> >
> >In fact JS has a good shortcut for your purpose:
> >
> > if(paramTwo == undefined)
> > paramTwo = someValue; // initialize default value
> >
> >becomes
> >
> > paramTwo = paramTwo || someValue[/color]
>
> I doubt that undefined would be a problem with any
> implementation of Javascript. On the other hand,
> both of your methods assume that zero, false, and
> "" are not valid parameter values.[/color]

Which is why it is probably best to test for precisely what the parameter
should be:

if (typeof paramTwo != 'string') {
paramTwo = 'default string';
}

- or -

if (typeof paramTwo != 'number') {
paramTwo = 0;
}

etc

--
| Grant Wagner <gwagner@agrico reunited.com>

* Client-side Javascript and Netscape 4 DOM Reference available at:
*

http://devedge.netscape.com/library/manuals/2000/javascript/1.3/reference/frames.html

* Internet Explorer DOM Reference available at:
*
http://msdn.microsoft.com/workshop/a...ence_entry.asp

* Netscape 6/7 DOM Reference available at:
* http://www.mozilla.org/docs/dom/domref/
* Tips for upgrading JavaScript for Netscape 7 / Mozilla
* http://www.mozilla.org/docs/web-deve...upgrade_2.html

**Dr John Stockton** · Jul 23 '05, 10:56 AM

Re: Is it possible to initialize function parameters in Javascript?

JRS: In article <40a31071$0$202 $75868355@news. frii.net>, seen in
news:comp.lang. javascript, Hiroshi Ochi <hiroshi_ochi@n ospam.com> posted
at Thu, 13 May 2004 06:06:42 :
[color=blue]
>Is it possible to initialize javascript function parameters (using MSIE
>6.0 and above)?[/color]
[color=blue]
>function myFunc(paramOne ,paramTwo="This is Default Message"){
> ...[/color]

Be aware that one can do something like

function myFunc(paramOne , paramTwo) {
if (!paramTwo) paramTwo = "This is Default Message"
....

But consider whether one might need to be able to supply such as 0,
false, NaN, ... for paramTwo.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
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**Lasse Reichstein Nielsen** · Jul 23 '05, 10:57 AM

Re: Is it possible to initialize function parameters in Javascript?

Lee <REM0VElbspamtr ap@cox.net> writes:
[color=blue]
> I doubt that undefined would be a problem with any
> implementation of Javascript.[/color]

In later versions of Javascript, "undefined" is merely a global
variable. In, e.g., IE 5, that variable was not defined, so writing
if (blah == undefined) ...
would give the undeclared variable error:
'undefined' is undefined
Kindof cute, really :)

/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

**Saint Jude** · Jul 23 '05, 10:57 AM

Re: Is it possible to initialize function parameters in Javascript?

Lee <REM0VElbspamtr ap@cox.net> wrote in message news:<c82kcj043 u@drn.newsguy.c om>...[color=blue]
> Saint Jude said:
>[color=green]
> >Comparing against undefined *may* be risky, and involve backward
> >compatibilit y problems. I'd go for: if(!paramTwo) - for an undefined
> >parameter test.
> >
> >In fact JS has a good shortcut for your purpose:
> >
> > if(paramTwo == undefined)
> > paramTwo = someValue; // initialize default value
> >
> >becomes
> >
> > paramTwo = paramTwo || someValue[/color]
>
>
> I doubt that undefined would be a problem with any
> implementation of Javascript. On the other hand,
> both of your methods assume that zero, false, and
> "" are not valid parameter values.[/color]

Lee, you are absolutely right about zero, false etc. I realised while
doing my laundry. That syntax is unfortunately unsafe to use.

Re: undefined

I'm not so sure about this. Perhaps you can put me straight.
According to MS JScript specification, undefined requries
JScript 5.5 (IE 5.5+). So I would suggest:
if(typeof(arg)= ="undefined" )
instead.

BTW, which is the safer to use - typeof operator, or typeof function ?

**Lasse Reichstein Nielsen** · Jul 23 '05, 10:57 AM

Re: Is it possible to initialize function parameters in Javascript?

thejuliankenned y@hotmail.com (Saint Jude) writes:[color=blue]
> BTW, which is the safer to use - typeof operator, or typeof function ?[/color]

There is no typeof function, only the operator.
Writing
typeof foo
and
typeof(foo)
is equivalent, just as
1+4
and
1+(4)
are. It's just a parenthesis around an expression.

/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

**Lee** · Jul 23 '05, 10:57 AM

Re: Is it possible to initialize function parameters in Javascript?

Saint Jude said:
[color=blue]
>I'm not so sure about this. Perhaps you can put me straight.
>According to MS JScript specification, undefined requries
>JScript 5.5 (IE 5.5+). So I would suggest:
>if(typeof(arg) =="undefined" )
>instead.[/color]

Yes, that's actually what I always use. I posted in haste.

**Dr John Stockton** · Jul 23 '05, 10:57 AM

Re: Is it possible to initialize function parameters in Javascript?

JRS: In article <c82kcj043u@drn .newsguy.com>, seen in
news:comp.lang. javascript, Lee <REM0VElbspamtr ap@cox.net> posted at Fri,
14 May 2004 07:16:51 :[color=blue]
>Saint Jude said:
>[color=green]
>>Comparing against undefined *may* be risky, and involve backward
>>compatibili ty problems. I'd go for: if(!paramTwo) - for an undefined
>>parameter test.
>>
>>In fact JS has a good shortcut for your purpose:
>>
>> if(paramTwo == undefined)
>> paramTwo = someValue; // initialize default value
>>
>>becomes
>>
>> paramTwo = paramTwo || someValue[/color]
>
>
>I doubt that undefined would be a problem with any
>implementati on of Javascript. On the other hand,
>both of your methods assume that zero, false, and
>"" are not valid parameter values.[/color]

Not quite; if one of them is a valid value then it can be the default.

P2 = 0
P2 = P2 || 0

results in P2 becoming the second 0 & no longer the first one, an
undetectable assignment.

ISTM that, in IE4,
X |= Y is X = X | Y
but X ||= Y is illegal. I wonder why.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

**Steve van Dongen** · Jul 23 '05, 10:58 AM

Re: Is it possible to initialize function parameters in Javascript?

Hiroshi Ochi <hiroshi_ochi@n ospam.com> wrote:
[color=blue]
>Hi Robert,
>
>Hmm, too bad. I think I'll just do the below workaround:
>
>
><html>
><script language="javas cript">
>function myFunc(paramOne ,paramTwo){
> if(paramTwo == undefined)
> paramTwo = someValue; // initialize default value
> ...
>}
></script>
></html>
>[/color]

x == undefined evaluates to true if x is null. Use typeof paramTwo ==
"undefined" if that matters to you.

Regards,
Steve

Is it possible to initialize function parameters in Javascript?

Is it possible to initialize function parameters in Javascript?

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