Identify null value using javascript

How do i identify null values using javascripts' length property
e.g.say mystring is variable holding the valueof my data to be tested.

mystring = <%=(Results.Fields.Item("Postion").Value)%>
If
(mystring.length=0)
document.write ("close to");
else
document.write (mystring & "is perfect");
)

please check whether the above code is correct. incase you find the answer please send mail to URL

You should have '==' in the if statement and not '='

Thankx
but i figured out the problem.
infact i should have had declared mystring = in " " which i didn't do it and hence there was error.