How to prevent changes to a prototype?

Question

In this code, the prototype can still change.

How I can prevent changes to the prototype?

var a = {a:1}
var b={b:1}
var c = Object.create(a)
Object.getPrototypeOf(c) //a
c.__proto__ = b;
Object.getPrototypeOf(c) //b
var d = Object.create(null)
Object.getPrototypeOf(d) //null
d.__proto__ = b;
Object.getPrototypeOf(d) //null

A prototype is just an object like every other one, meaning that you can freeze/seal it. — Bergi, Nov 11 '16 at 23:23
`__proto__` is deprecated. Use `Object.setPrototypeOf` if you have to. — Bergi, Nov 11 '16 at 23:24

score 6 · Accepted Answer · edited Dec 13 '16 at 18:51

How I can prevent changes to the prototype?

I assume you are not talking about mutating the prototype object itself, but overwriting the prototype of an existing object.

You can use Object.preventExtensions() to prevent that:

var a = {a:1}
var b = {b:1}
var c = Object.create(a)
Object.preventExtensions(c) 
console.log(Object.getPrototypeOf(c)) //a
c.__proto__ = b; // Error

But that also means you cannot add any new properties to it. You could also use Object.freeze() or Object.seal() depending on your needs, which restrict modifications to the object even more.

There are no other ways though.

score 0 · Answer 2 · answered Nov 11 '16 at 23:21

Yes we can ,use Object.freeze.

Object.freeze() method freezes an object: that is, prevents new properties from being added to it; prevents existing properties from being removed; and prevents existing properties, or their enumerability, configurability, or writability, from being changed. In essence the object is made effectively immutable. The method returns the object being frozen.

See this freeze reference

check this snippet

var a = {a:1}
var b={b:1}
var c = Object.create(a)
Object.getPrototypeOf(c) //a
Object.freeze(c);
c.__proto__ = b;//throws error now
console.log(Object.getPrototypeOf(c)) //a
var d = Object.create(null)
Object.getPrototypeOf(d) //null
d.__proto__ = b;
Object.getPrototypeOf(d) //null

Hope this helps

How to prevent changes to a prototype?

2 Answers2