Question 1

What is the difference between state and props in React?

Accepted Answer

Props are values a parent passes to a child, and they are read-only inside the child. State is data owned by a component, which it can change with its setter function. When state changes, React re-renders that component. A common design rule is to keep state as high as needed and pass it down through props, so data has one clear owner.

Question 2

Why does a React list need a key for each item?

Accepted Answer

A key gives React a stable identity for each item, so it can match old and new items between renders and update only what changed. Without keys, React has to guess which items moved, which can cause wrong state to appear on the wrong row. Use a unique, stable id from your data, not the array index when items can be reordered or removed.