React: What is React virtual DOM diffing?

Diffing algorithm:

• Compare old and new virtual DOM trees
• Find minimal set of DOM operations
• O(n) using heuristics

Heuristics:

1. Different type -> destroy and rebuild
2. Same type -> update props
3. Keys identify list items

1// React compares:
2// Old: <div className="a" />
3// New: <div className="b" />
4// Result: update className only

Performance: Not O(n^3) like generic tree diff. Heuristics make it practical.

Optimizations: Avoid changing component types, use stable keys, minimize state changes.