How can I change a JS element to see if it is a node or an empty variable?
It depends on what you mean by an empty variable.
If you mean it hasn't had a value assigned, you can check for
alert( someVariable !== "undefined" );
Or if you know it has a value, and need to see if it is an element, you could do something like this:
alert( someVariable && someVariable.nodeType );
Or if you need to verify that it is a type 1 element, you could do this:
alert( someVariable && someVariable.nodeType === Node.ELEMENT_NODE );
This eliminates text nodes, attribute nodes, comments, and a bunch of others.