Another way to do it (this is how I have done it recently) is to check & then assign like you do, but the check I do is a little different. I do a typeof() on the variable — if it returns ‘object’ then I must have the element, if it returns ’string’ then I must just have the ID, if it returns ‘undefined’ then the variable has been initialized but not defined, or doesn’t exist at all.

So the one line would look like:
if(typeof(foo) != ’object’) foo = document.getElementById(foo);

(Now that I look at it, I think it’s even longer doing it this way than how you do it.)
Anyway, it’s just another way of doing the same thing. Thanks for the ‘one line’.