Condition Always true when checking for "undefined" in Javascript

[vuyiswamb]

Good Day all

i am reluctantly maintaining a Classic Asp application that will be re-written in few months to come. i have an issue where i have a Code like this

   if(document.frmEntry.optMethod != "undefined")
                        {
                            if (document.frmEntry.optMethod.selectedIndex == 0) {
                                strPrompt=strPrompt+'Please specify the Valuation Method\n';
                                if ( objFocus == null ) {
                                    objFocus = document.frmEntry.optMethod;
                                }
                            }
                        } 

my problem here is that even if document.frmEntry.optMethod is not equal to undefined the code still go into the condition as if it was true. i have attached a proof in my debuger.

http://www.vetauinvest.com/Example/IE_DEBUGGER.png

Thanks

[Dani]

What have you attached???

[vuyiswamb]

hi Dani

i have updated the post. please check the link

[AleMonteiro]

Your problem is simple... if(document.frmEntry.optMethod != "undefined") this is testing if an object, that may not exist (undefined) is different than an string with value "undefined".

Two ways to resolve it:

if( typeof document.frmEntry.optMethod != "undefined" )

OR

if(document.frmEntry.optMethod != undefined )

[Airshow]

Or, simplest of all :

if( typeof document.frmEntry.optMethod ) {
    ...
}

[Airshow]

Sorry, that shoud read :

if( document.frmEntry.optMethod ) {
    ...
}