How to prevent a property from being removed or modified?

Question

I have an object and would like to prevent certain properties from being modified or removed. The code below is to illustrate:

var pessoa = {
  nome: 'Fulano de Tal',
  doc: '999.999.999-99'
};

console.log(pessoa);
pessoa.doc = '111.111.111-11'; // Modifica
console.log(pessoa);
delete pessoa.doc; // Remove
console.log(pessoa);

It is possible to prevent these actions ?

Answer 1

You can use the method Object.(), which prevents object properties from being removed or modified (transforms object into read-only -- read-only), also preventing new properties from being added.

Syntax: Object.freeze(pessoa);

In strictly speaking ("use strict";) will return errors:

var pessoa = {
  nome: 'Fulano de Tal',
  doc: '999.999.999-99'
};

pessoa.doc = '111.111.111-11'; // Modifica
Uncaught TypeError: Cannot assign to read only property

delete pessoa.doc; // Remove
Uncaught TypeError: Cannot delete property

pessoa.idade = '23'; // Adiciona
Uncaught TypeError: Cannot add property idade, object is not extensible

Answer 2

Yes, there is a way to create an immutable variable using es5.

const object1 = {};

Object.defineProperty(object1, 'property1', {
  value: 42,
  writable: false
});

object1.property1 = 77;
// throws an error in strict mode

console.log(object1.property1);
// expected output: 42

This is the same example that the documentation itself uses in: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty