Answer
Keyed diffing builds a keyed map to detect moves, deletions, and insertions. Non-keyed diffing assumes positional alignment, which is faster but incorrect for reordering.
Quick Answer
For keyed lists, React builds a map of key → fiber, then matches new elements to existing fibers by key — O(n) instead of O(n²) comparison. For non-keyed lists, React compares by position. Keys allow React to detect moves, insertions, and deletions precisely, reusing DOM nodes for moved items instead of destroying and recreating them.
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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