How do I deep clone an object in JavaScript without JSON.parse(JSON.stringify())?
asked 4 months ago199 viewsen
I've been using JSON.parse(JSON.stringify(obj)) to clone state, but it breaks Date objects and drops undefined and Map values. Is there a built-in way now?
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2 Answers
Yes. structuredClone is built into all modern browsers and Node 17+:
const copy = structuredClone(original);It correctly handles Date, Map, Set, RegExp, typed arrays, ArrayBuffer, and even circular references.
It can't clone functions, DOM nodes, or class prototypes: a class instance comes back as a plain object. If you need those, use a library like lodash.clonedeep, or rethink whether you need a deep clone at all. In React, immutable updates with spreads are usually enough.
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Often you don't need a *deep* clone. For updating nested state, a targeted shallow copy is cheaper and clearer:
const next = { ...state, user: { ...state.user, name: 'Ruth' } };For very nested state, immer's produce lets you write mutations that produce an immutable copy.
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