selectors.js

const getAllFooNames1 = createSelector(
  stateTree => stateTree,
  stateTree => {
    return stateTree.allFoos.map(foo => foo.name);
  });

const getAllFooNames2 = createSelector(
  stateTree => stateTree.allFoos,
  allFoos => {
    return allFoos.map(foo => foo.name);
  });