mapEach

Lifts one item transform into a list transform.

const toUser = rename({user_id: 'id'});
const toUsers = mapEach(toUser);

toUsers([{user_id: 1}, {user_id: 2}]);
// [{id: 1}, {id: 2}]

null and undefined inputs return an empty array:

toUsers(null); // []

The returned array is new, and each item is transformed in order. Inputs other than an array, null, or undefined are outside the function's contract.