JavaScript
Deep Clone
Copy a nested structure so nothing is shared — including the cases that break a naive recursion.
JavaScript · ES6 — Pratik Rai ·
#Objects#Immutability
Make Object Immutable
Freeze an object all the way down, because Object.freeze only handles the top level.
By Pratik RaiMedium
Write deepFreeze(obj) that freezes an object and everything nested inside it, then returns the same object.
After freezing, writing to a property at any depth must not change it. A structure that contains itself must not recurse forever.
Examples
Input:
JSfile.javascript1const config = deepFreeze({ api: { retries: 3 } }); 2config.api.retries = 99; 3config.api.retries;
Output:
3
Object.freeze alone would have left the nested object writable.
Constraints
- Values are objects, arrays and primitives
Notes
- In sloppy mode a write to a frozen property fails silently; only strict mode throws.
- Freeze before recursing and
Object.isFrozenbecomes your cycle guard for free.
Goal: Freeze every level and return the same object.
Source
Frequently asked questions
- Is Object.freeze deep?
- No. It prevents writes to the object's own properties only, so any nested object stays fully mutable. That makes an unfrozen nested structure a false guarantee.
- Why freeze before recursing?
- Because it makes a self-referencing object terminate. By the time the walk reaches it again it is already frozen, so an `Object.isFrozen` check doubles as the cycle guard.
- Why does writing to a frozen object fail silently?
- In sloppy mode a failed write is ignored without any error. Only strict mode — including module code — throws a `TypeError`, which is why the behaviour surprises people in a console.
- Is deep freezing expensive?
- It walks and freezes every nested object once, which is real work on a large structure, and it cannot be undone. For big application state, structural sharing or an immutability library is usually a better fit.
Related Challenges
Continue learning with these related challenges
JavaScript
Deep Equality
Compare two values structurally, because === only ever compares references.
JavaScript · ES6 — Pratik Rai ·
JavaScript
Array.prototype.groupBy
Group an array into buckets by a key function — now a real language feature as Object.groupBy.
JavaScript · ES6 — Pratik Rai ·
JavaScript
Deep Clone
Copy a nested structure so nothing is shared — including the cases that break a naive recursion.
JavaScript · ES6
Pratik Rai ·
JavaScript
Deep Equality
Compare two values structurally, because === only ever compares references.
JavaScript · ES6
Pratik Rai ·
JavaScript
Array.prototype.groupBy
Group an array into buckets by a key function — now a real language feature as Object.groupBy.
JavaScript · ES6
Pratik Rai ·