in todo/data/database.js [128:147]
export function removeCompletedTodos(): $ReadOnlyArray<string> {
const todoIdsForUser = getTodoIdsForUser(USER_ID);
const todoIdsToRemove = getTodos()
.filter((todo: Todo): boolean => todo.complete)
.map((todo: Todo): string => todo.id);
// Remove from the users list
todoIdsByUser.set(
USER_ID,
todoIdsForUser.filter(
(todoId: string): boolean => !todoIdsToRemove.includes(todoId),
),
);
// And also from the total list of Todos
todoIdsToRemove.forEach((id: string): boolean => todosById.delete(id));
return todoIdsToRemove;
}