What are the good practices for conditional variable assigning?

My example

I have a string, that may be empty ("") or equal to "foo".

I want to create a variable my_string and assign to it the value "foo" of the string, or a value "empty" when the string is empty.

var my_string = string == "";
my_string = (string === "") ? "empty" : string;

Or

(string === "") && var my_string = string;

Are these good ways of doing what I am asking?

What are the recommended syntax for this case?