Rendering a List

What this is. React renders arrays of elements. So to show a list, turn your data into an array of elements with map.

Why map and not forEach. map returns a new array. forEach returns nothing, so it renders nothing. This is one of those bugs where the code looks entirely reasonable and the screen is simply empty.

✦ The arrow must return

books.map(b => <li>...</li>) returns each element. books.map(b => { <li>...</li> }) returns undefined, because braces open a function body rather than wrapping an expression. If you use braces, you must write return.