reducers

reducers.js

const state = {
  users: {
    list: {id1: user1, id2: user2},
    followers: {id1: [id2], id2: [id1]},
    following: {id1: [id2], id2: [id1]},
    interestingPersons: {id1: [id2], id2: [id1]},
    ...
  }
}

...

class MyComponent {
  render() {
    const { users } = Store.getState();
    // how to get followers and followings for user id=id1 ?
    // this way:
    const followers = users.followers[id1].map((id) => {state.list[id]});
    const followings = users.followings[id1].map((id) => {state.list[id]});
    // the problem is: I know inside my component about state structure. 
    // But I want to know about it only in reducers
    // cause this is the place when data changes.
  }
}

Use composable selectors: http://github.com/faassen/reselect
These are the same as NuclearJS “getters”: https://github.com/optimizely/nuclear-js#getters

Thanks a lot, @gaearon!