Unit is a subtype of scala.AnyVal. There is only one value of type Unit, (), and it is not represented by any object in the underlying runtime system. A method with return type Unit is analogous to a Java method which is declared void.
void is a Java keyword.
Used at method declaration and definition to specify that the method does not return any type, the method returns void. It is not a type and there is no void references/pointers as in C/C++.
A variable that has not been assigned a value is of type undefined. A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned.
undefined(in JS) ~void(in Java) ~Unit(Scala)Maybe you meant expressions vs statements
Statement:
Expression: