Keys and list reconciliation

Keys tell React which item is which. Using an array index means insertions silently reassign state to the wrong row.

What this lesson covers

• Use stable identity for keys, never the array index
• Understand how reconciliation matches elements between renders
• Diagnose lost input state in a reordered list

This lesson sits in Rendering Optimization, part of React Performance Engineering. It assumes what came before it and leads directly into the next lesson in the module.