[Javascript] how can I check to see if a text box has a number or a string in it???

[Scott.Wiseman]

I am using a frame...

and I am checking the bottom text box "ClosingYear"
from the top frame...

I get an error..

is this not the correct way to use the function????

//  if( isNaN(parent.TransDetail.myform.ClosingYear.value)==true )
//        {
//            alert("You must select a Year");
//        return false;
//        }