How to call a variable that references to a function

Please see my comment to the question.

Of course, wrap1 is a variable, but it means nothing. A variable can be a function or non-function. Function is also on object. Let's see.

var wrap1 = wrapValue(5);

means that wrap1 is assigned to some object returned by function wrapValue. So, let's see what this function returns. As you can see, it returns another function. In other words, returned object is a function function object. Unlike other objects, this kind of object supports the operation "call". And the syntax wrap1() is just the syntax call.

The question "why no just wrap1?" simply makes no sense. Both wrap1 and wrap1() are two different expressions; both are correct and return totally different objects: first return the result of the function call, the type if this result is defined by n passed during the call to wrapValue; second returns a parameterless function function object which, in turn, can return the object of the same type. Compare

var myObject = wrap1; // some parameterless function
var myOtherObject = wrap1(); // some object, same as n
// you can call
var someObject = myObject(); // because this is a function object
//someObject will be the same as myOtherObject

Are you getting the idea?

—SA