User reactions with helper

userReactions2.js

// I call the helper `d` after the concept `domain`.
const d = () => freezer.get().user;

freezer.on('user:create', user => {
  d().set(user.id, user);
});

freezer.on('user:update', (id, update) => {
  d()[id].set(update);
});

freezer.on('user:delete', id => {
  d().remove(id);
});