由new构造函数创建的函数对象是否在javascript中被视为可变对象？

Question

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??

Answer 1

JavaScript don't have "immutable objects" there 2 types:

1) primitives - immutable

2) Object - mutable

update: object freeze can give some "immutable"

Answer 2

It is mutable, as you can see from this working example.

 var Node = function(data) { this.data = data; this.next = null; }; var v = new Node(0); v.myNewAttribute = 'foobar'; var elemDiv = document.createElement('div'); elemDiv.innerHTML = JSON.stringify(v); document.body.appendChild(elemDiv); 

Answer 3

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)

Answer 4

v is a mutable object. To change this object to an immutable object use the Object.freeze() method.

Example:

 var Node = function(data) { this.data = data; this.next = null; }; var v = new Node(0); // "v" object is mutable v.data = 1; // The "data" property value will change console.log(v); Object.freeze(v); // "v" object is immutable v.data = 2; // The "data" property value will NOT change console.log(v); 

The Object.freeze() method freezes an object. A frozen object can no longer be changed; freezing an object prevents new properties from being added to it, existing properties from being removed, prevents changing the enumerability, configurability, or writability of existing properties, and prevents the values of existing properties from being changed. In addition, freezing an object also prevents its prototype from being changed. freeze() returns the same object that was passed in. more