---
title: deepFreeze
tags: object,recursion,intermediate
---

Deep freezes an object.

Use `Object.keys()` to get all the properties of the passed object, `Array.prototype.forEach()` to iterate over them.
Call `Object.freeze(obj)` recursively on all properties, checking if each one is frozen using `Object.isFrozen()` and applying `deepFreeze()` as necessary.
Finally, use `Object.freeze()` to freeze the given object.

```js
const deepFreeze = obj => {
  Object.keys(obj).forEach(prop =>
    obj[prop] = typeof obj[prop] === 'object' && !Object.isFrozen(obj[prop]) ? deepFreeze(obj[prop]) : obj[prop]
  );
  return Object.freeze(obj);
}
```

```js
'use strict';

const o = deepFreeze([1, [2, 3]]);

o[0] = 3; // not allowed
o[1][0] = 4; // not allowed as well
```