This content originally appeared on DEV Community and was authored by Aman Kureshi
When rendering lists in React, you’ll often see a warning about missing keys. But why are keys so important? 
Example without key:
{items.map((item) => (
<li>{item}</li>
))}
React struggles to identify which item changed, added, or removed.
Example with key:
{items.map((item) => (
<li key={item.id}>{item.name}</li>
))}
React can track each element efficiently.
Key Points:
• Keys help React optimize re-rendering.
• Always use a unique identifier (like id).
• Avoid using index as key, unless items never change order.
Think of keys as React’s way of labeling items so it knows what’s what during updates. 
This content originally appeared on DEV Community and was authored by Aman Kureshi