Is function object created by `new` constructor treated as mutable object in javascript?

From study, I understood that in javascript, mutable objects() are treated by call-by-reference, and immutable objects are treated by call-by-value calling convention.

Let's say I use this kind of data,

var Node = function(data) {
  this.data = data;
  this.next = null;
};

var v = new Node(0);

is v a mutable object or an immutable object??

First of all lets understand what is the new operator doing inside the created execution context behind the scenes:

It will:

1. Create a new Object (and attach it to the this label)
2. That new object's __proto__ property will reference the function's prototype property
3. It will return the newly created object (if you are not explicitly returning an object)

So in your case:

var v = new Node(0);

v is actually an Object (the one that created and returned via new) and objects in JavaScript are mutable.

Here are the primitives (immutable) types:
Boolean
Null
Undefined
Number
String
Symbol (new in ECMAScript 6)