Why is React showing "each child should have a unique "key" prop" error on console?

Question

I'm trying to create a react app and on console showing this error, what does it mean?

react-jsx-dev-runtime.development.js:87 Warning: Each child in a list should have a unique "key" prop.

I want solution of this react problem

Answer 1

when you're using .map(), you should provide a unique key for each of the elements that you render.

[1,2,3].map(item => <div key={item}>item</div>);