Reference to undefined property

[jehoshua]

Hi,

I'm getting the following messages from the (Mozilla) Javascript console.

Warning: reference to undefined property CategoryList[frm.selCategory.value]
Source File: http://sitename/rep/new.asp
Line: 209

Error: CategoryList[frm.selCategory.value] has no properties
Source File: http://sitename/rep/new.asp
Line: 209

Line 209 (shown in red)is in the following code:

function getSubCategories(categoryid)
  {
  var subcat = null;
  if ( frm.selCategory.value == null ) {
     subcat = "0";
     }
  else {
     subcat = CategoryList[frm.selCategory.value].categoryid;  // Line 209
     }
  var current = (frm.selSubCategory.value) ? SubCategoryList[frm.selSubCategory.value].subcatname : '';
	    
  for(z = frm.selSubCategory.length - 1; z >= 0; z--)
     {
     frm.selSubCategory.options[z] = null;
     }
  for(z = 0; z < SubCategoryList.length; z++)
     {
     var prod = SubCategoryList[z];
     if(prod.categoryid == subcat)
          { 
          frm.selSubCategory.options[frm.selSubCategory.options.length] = new Option(prod.subcatname, z, (prod.subcatname==current), (prod.subcatname==current));
          }
     }
  
  frm.category.value = CategoryList[frm.selCategory.value].categoryid;
  }

frm.selCategory.value is showing as null, when I do a 'Page Info' , and I would have thought that by doing:

if ( frm.selCategory.value == null ) {

to be suffient for a test. I have also tried:

if ( frm.selCategory.value = null ) {
// and ...
if ( frm.selCategory.value ) {

but still no luck. I _think_ the problem lies where the dropdown is "emptied":

frm.selSubCategory.options[z] = null;

which of course is followed by code to then "fill" the dropdown (there are 3 levels of dropdowns, a hiearchy). In some circumstances, the top level selection may not find any lower level values, and so, the subcategory dropdown list will remain empty (null ?),. How do I check if the list is null, is it:

If frm.selSubCategory.options.length ==0

One way or another the frm.selCategory.value is an "undefined property", and then later an error stating "has no properties". If I can check whether the property is undefined (or exists ??), then just one line of code:

frm.SelGroup.options[frm.SelGroup.options.length] = new Option('Unknown', '0');

with the default value for unknown/unused will suffice. I just don't know how to check for the property. (I guess it is part of an object ??).

Thanks,

Peter

[MikeFoster]

Here's something I use. It returns true if all it's arguments are defined.

function xDef() {
  for(var i=0; i<arguments.length; ++i){if(typeof(arguments[i])=="undefined") return false;}
  return true;
}

[jehoshua]

Hi Mike,

Thanks a lot, your code did the trick.

Because (being fairly new to JS) I needed to understand the code, I reformatted it to:

function xDef()
   {
     for(var i=0; i<arguments.length; ++i)
     {  
       if(typeof(arguments[i])=="undefined" ) {
          return false;
       }
       else {
          return true;
       }
     }
   }

and call the function like this:

var dropdown = null;
dropdown = xDef(frm.selCategory.value);

if (dropdown) {
   subcat = CategoryList[frm.selCategory.value].categoryid;
   }
else {
   subcat = "0";
   }

It's working okay, but I noticed in Javascript Console a warning message:

Warning: function xDef does not always return a value
Source File: http://sitename/rep/new.asp
Line: 310, Column: 6
Source Code:
}

which is the last line of the function 'xDef'

Thanks a lot,

Peter

[Anarchos]

You reformatted it incorrectly. Look at where the braces are in the original version.

[MikeFoster]

Nice work, jehoshua.

But, your function won't work if it is passed more than one argument.

Here are a some different formatting styles:

function xDef() {
  for(var i = 0; i < arguments.length; ++i) {
    if (typeof(arguments[i])=="undefined" ) {
      return false;
    }  
  }
  return true;
}

function xDef()
{
  for(var i = 0; i < arguments.length; ++i) {
    if (typeof(arguments[i])=="undefined" ) {
      return false;
    }  
  }
  return true;
}

function xDef()
{
  for(var i = 0; i < arguments.length; ++i)
  {
    if (typeof(arguments[i])=="undefined" )
    {
      return false;
    }  
  }
  return true;
}

This last one I consider an 'old' style. I think it is confusing. Nevertheless, I am currently working on some 'legacy' C code which uses this style.

function xDef()
  {
  for(var i = 0; i < arguments.length; ++i)
    {
    if (typeof(arguments[i])=="undefined" )
      {
      return false;
      }  
    }
  return true;
  }

[Vincent Puglia]

Hi,

I tend to prefer having only 1 exit point and as few braces as possible:

function xDef()
{
var retVal = true;
for(var i = 0; i < arguments.length; ++i)
if (typeof(arguments[i])=="undefined" ) 
retVal = false;
return (retVal); 
}

Vinny

[jehoshua]

Hi,

You reformatted it incorrectly. Look at where the braces are in the original version.

Yes, I didn't realise the return true; was outside the FOR loop. I'm much more used to application programming where there is a definite 'end' like:

Do while condition
... do some stuff
End do

For (iteration constraints)
... do some stuff
End  (or End for)

If (condition) then
 ... do some stuff
else
  ... do other stuff
End  (or EndIf or End If)

Peter

[jehoshua]

Hi Mike,

Thanks for your examples. The third one you posted was how the code eventually worked out, sio I guess that makes me 'old'.

Peter

[jehoshua]

Hi Vinny,

I tend to prefer having only 1 exit point and as few braces as possible:

It was hard to distinguish, though (for me) if the:

return (retVal);

was inside or outside the FOR loop, and especially with no indenting and no braces, I found I had to look at it for a lot longer to understand what it was doing. Finally it clicked though, true will always be returned, unless the IF condition is met.

I like the braces, they keep my pants up.

Thanks,

Peter

[MikeFoster]

I like the braces, they keep my pants up.

[MikeFoster]

I tend to prefer having only 1 exit point...

It is indeed better design. I might do it like this then:

function xDef() {
  var ret = true;
  for (var i = 0; i < arguments.length; ++i) {
    if (typeof(arguments[i])=="undefined" ) {
      ret = false;
      break;
    }  
  }
  return ret;
}

This is the way I usually format my javascript. For C/C++ it depends on the history of the project, and if there were coding/formatting conventions used by the previous developer/team.

Formatting is like naming conventions and editors... everyone has their favorite but 'consistency' is more important than anything.

[Vincent Puglia]

Hi,

was inside or outside the FOR loop, and especially with no indenting and no braces

Re the lack of indentation: I plead innocence!! When I wrote the code, it was indented. I evidently had some problems with the forum's quick reply; it even stuck my name within the 'code' elements.

Re the lack of braces: I learned javascript via C and a few other languages. Result: I always look for the semi-colon ";" I tend to use braces only when there is a chance for confusion (multiple embedded if/elses)

I like the braces, they keep my pants up.

Gee, and I thought they were for teeth

Vinny

[MikeFoster]

[jehoshua]

Hi,

There was one final (little) bug that had me stumped for a while, so thought to share it. The function:

function xDef()
  {
  var retval = true;
  for(var i=0; i<arguments.length; ++i)
  {  
     if(typeof(arguments[i])=="undefined" )
     {
     retval = false;
     break;
     }
  }
  return (retval);
  }

wouldn't work when a 'option' (dropdown) was empty. With JS debugger and stepping through the code, the properties of two dropdowns were:

selCategory
length 6
selectedIndex 3
value "7"
options.length 6
options.selectedIndex 3

selSubCategory
length 0
selectedIndex -1
value ""
options.length 0
options.selectedIndex -1

The dropdown selCategory had values in it, and the dropdown selsubCategory did not (empty). Therefore, the FOR loop in function XDEF wouldn't get executed, because the length was zero for selSubCategory.

No doubt if I just change it to:

function xDef()
  {
  var retval = true;
  if (arguments.length == 0)
  {   
     retval = false;
  }
  for(var i=0; i<arguments.length; ++i)
  {  
     if(typeof(arguments[i])=="undefined" )
     {
     retval = false;
     break;
     }
  }
  return (retval);
  }

... that should fix it.

Thanks,

Peter