Incorrect use of id function in React

It is incorrect to generate id directly in the attribute, like this:

jsxconst res = prods.map(function(prod) {
  return <p key={id()}>
    <span>{prod.name}</span>
    <span>{prod.cost}</span>
  </p>;
});

The reasons for this will become clear to you in the following lessons. For now, just keep in mind that this is wrong and should never be done.