What are reconciliation, Fiber and keys?

Definition:

Reconciliation is how React matches elements from the previous and next render to decide what to keep, update or replace. Fiber is the internal representation that helps React organize that work. Keys supply identity among siblings, allowing React to preserve the right state as a list changes.

Key points:

• Reconciliation matches the old and new component trees.

• Fiber is React's internal structure for organizing and scheduling work.

• Stable keys help preserve list-item identity; avoid indexes for reorderable lists.

• Changing a key can deliberately reset a subtree's state; random keys reset identity on every render and cause unnecessary remounts.

Interview point:

• A key is about identity, not just removing a console warning. Demonstrate a reordered list with editable rows.