Answer
The render phase only calculates changes and contains no side effects, making it pure. The commit phase applies changes to the DOM, causing side effects and making it impure.
Quick Answer
The render phase is pure — React may run it multiple times, discard results, or run it in parallel. No DOM mutations happen here. The commit phase is impure — React applies all DOM changes in one go. This two-phase design lets React interrupt rendering safely while guaranteeing that DOM updates are atomic and consistent.
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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