Creating a 'const const' object in javascript [duplicate]

Question

In javascript, if I create a const array, I can still modify the object the variable points to:

// The const declaration creates a read-only reference to a value. 
// It does not mean the value it holds is immutable—just that the variable identifier cannot be reassigned.
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const
const x = [1,2,3];
x.push(4);
console.log(x);
x=55 // But this is illegal and will error
console.log(x);

Is there a way to make the elements in an array immutable as well? Similar to something like const int* const x; in C?

Object.freeze(x) will work

John
– John

2022-02-04 01:02:06 +00:00
Commented Feb 4, 2022 at 1:02 — John
– John, Commented Feb 4, 2022 at 1:02

Caleb Denio · Accepted Answer · 2022-02-04 01:01:19Z

4

You can use Object.freeze to prevent an object (or array) from being changed:

const x = [1, 2, 3];
Object.freeze(x);

x.push(4); // This will throw an exception

answered Feb 4, 2022 at 1:01

Caleb Denio

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John · Accepted Answer · 2022-02-04 02:28:38Z

1

objects frozen with Object.freeze() are made immutable.

Here are the docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze

Example:

const x = [1,2,3];
Object.freeze(x);

edited Feb 4, 2022 at 2:28

answered Feb 4, 2022 at 1:02

John

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