Answer
React relies on reference comparison. Mutating nested objects keeps the same reference, preventing re-rendering. Spreads or immutable helpers create new references.
Quick Answer
Nested state (objects with nested objects) shares references. If you spread only the top level, nested objects still share the same reference — other parts of state pointing to them see the mutation. Deep cloning everything is expensive. Use Immer (or manual spreading at each level) to create truly independent state copies.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ