Key
Key — Is a special string attribute you need to include when creating lists of elements.
Keys help React identify which items have changed, are added, or are removed.
const numbers = [1, 2, 3, 4, 5];
const listItems = numbers.map((number) =>
<li key={number.toString()}>
{number}
</li>
);
When you don’t have stable IDs for rendered items, you may use the item index as a key as a last resort.