61106 - Receiving "undefined" as element.tagName in the following script exits the script

Status: VERIFIED INVALID

(Core :: JavaScript Engine, defect, P3)

Description

[Cormac F]

Whenever I try to run the script detailed below, the script is terminated at 
the first entry into the for loop. I have traced this back to the .tagName 
method.Whenever "undefined" is returned for this, it exits the script even 
though I am testing for "undefined" in the first If statement.
I can't upload an example because of college proxy settings, but heres a 
snippet of the code:

...
for(i=0;i<parentDiv.childNodes.length;i++){
    var current = parentDiv.childNodes[i];
     if(current.tagName!="undefined"){
	  if(current.style.display!="none")
		current.style.display="none";
	  else
		current.style.display="";
      }
}
...

parentDiv is a var that just holds the parent node of the object the script 
acts upon.This for loop does not execute past the first if statement

Comment 1

[Phil Schwartau]

I think you've got to check for the value undefined, not the string "undefined".
For example, in the standalone JS shell, testing for an uninitialized variable:


js> var x

js> x == undefined
true
js> x == "undefined"
false


js> x != undefined
false
js> x != "undefined"
true



Please let us know what happens if you replace your test 

                 if(current.tagName!="undefined")

with:            if(current.tagName!= undefined )  



Thanks -

Comment 2

[Cormac F]

As soon as I posted, I realised the mistake and tried it with ==null 
instead.This returned true, yet the script still didn't work.Now, using 
==undefined, the script is working again. Label this one a false alarm, 
perhaps, blamed on a too hasty bug reporter! Apologies for the error. 
Still, should there be a difference between the action of null and undefined?

Comment 3

[Cormac F]

and now, a minute later, null appears to work correctly (IE5 doesn'y know 
undefined).Oh, blame it on the late hour (its 1am over here).I'm sorry about 
this.But honestly, it didn't work the first time!

cflynn

Comment 4

[Phil Schwartau]

No problem - glad everything is working. Thanks for using Bugzilla!
Have to resolve this bug as invalid, however - 

Comment 5

[Phil Schwartau]

Marking Verified -