What is the difference between a variable with an empty string and a variable with a value of undefined?

Question

Is var empty= " "; == var empty;?

Answer 1

No, it's not the same. If you declared a variable, you only reserve some memory (as much as required, depending on the data type) for later use. If you assign an empty string, it has a concrete value, which is stored within the reserved memory. You could learn some C for better understanding.