li key attribute
//A “key” is a special string attribute you need
//to include when creating lists of elements.
function NumberList(props) {
const numbers = props.numbers;
const listItems = numbers.map((number) =>
<li key={number.toString()}> {number}
</li>
);
return (
<ul>{listItems}</ul>
);
}
const numbers = [1, 2, 3, 4, 5];
ReactDOM.render(
<NumberList numbers={numbers} />,
document.getElementById('root')
);