optional function parameters

[RobBroekhuis]

I'm unclear on the syntax for defining a function with optional parameters. One reference I found digging through the web suggested this should work:

function ref(url,linkname,extra='')
{
window.document.write('<a href=

http://&quot;'+url+'&quot;

target=&quot;resource&quot;>'
+linkname+'</a>'+extra);
}

but IE throws an error. How should I rewrite this?


Rob

 

[woja]

   function ref(url, linkname, extra) {
      if (extra == null) {
         extra = ""
      }
      window.document.write('<a href=[URL unfurl="true"]http://&quot;;'+url[/URL] + '&quot; target=&quot;resource&quot;>' + linkname + '</a>' + extra);
      return;
    }

That's one way to do it.
OK?

________________________________________
Roger J Coult; Grimsby, UK
In the game of life the dice have an odd number of sides.

 

[kaht]

I just wanted to throw in a cool trick. Instead of using:

if (extra == null) {

you can use:

if (!extra) {

to check for the existance of a value.

-kaht

 

[RobBroekhuis]

woja, kaht,
Yeah, that's the approach I did take (kaht's actually). I just came across the other syntax on the web and was wondering if I could use it. I think the particular page was describing Javascript 2.0


Rob

 

[woja]

There's a problem with using kaht's solution, in general (it's ok with strings) but:

   function mult1(aNumber, aBase) {
      if (!aBase) aBase = 1;
      return aNumber * aBase;
   }
   function mult2(aNumber, aBase) {
      if (aBase == null) aBase = 1;
      return aNumber * aBase;
   }
   window.alert("1. " + mult1(10));
   window.alert("2. " + mult2(10));
   window.alert("3. " + mult1(10, 0));
   window.alert("4. " + mult2(10, 0));

Will display:
[tt]
1. 10
2. 10
3. 0
4. 10
[/tt]
because [tt]0[/tt] will cause the [tt]aBase[/tt] argument to be changed to [tt]1[/tt] in [tt]mult1()[/tt]. Omitted arguments in a function always have the value [tt]null[/tt] but other values than [tt]null[/t] are treated as [tt]false[/tt] and cause the &quot;optional argument&quot; code to be evoked using kaht's method.

Hope this helps.

________________________________________
Roger J Coult; Grimsby, UK
In the game of life the dice have an odd number of sides.

 

[woja]

Whoops!:

because [tt]0[/tt] will cause the aBase argument to be changed to [tt]1[/tt] in [tt]mult1()[/tt]. Omitted arguments in a function always have the value null but other values than [tt]null[/tt] are treated as [tt]false[/tt] and cause the &quot;optional argument&quot; code to be evoked using kaht's method.

Hope this helps.


________________________________________
Roger J Coult; Grimsby, UK
In the game of life the dice have an odd number of sides.

 

[tanderso]

Roger, I would consider multi1 to have the correct behavior. If you multiply 10 by nothing, you should get zero, not 10. In other words,

if (!aBase) aBase = 0;

is correct.

Sincerely,

Tom Anderson
Order amid Chaos, Inc.

http://www.oac-design.com

 

[woja]

Whoops, I got the answers wrong.
[tt]mult1[/tt] would display [tt]10[/tt] in 3 and [tt]mult2[/tt] would display [tt]0[/tt] in 4. That makes us both right, Tom.

Soryy for the error (should have checked).


[tt]________________________________________________________________
Roger
Life is a game of cards in which the deck contains only jokers.[/tt]