combine-section-selectors

Combines selectors into one object with proper path handling.

API

Every selector should have get prefix in name! E.g. getMyValue.
Also names of all selectors should be uniq.

default export:

(modules: {[string]: {[string]: Function}}) =>
    ({[string]: Function})

Name of module should be exact same as key on where state is stored. So if you have state.users.userId, you should combine selectors for users on "users" key:

const fromState = combineSelectors({
    users: {
        getUser: (users, userId) => users[userId],
    },
});
fromState.getUser({users: {myId: {}}}, `myId`)

Selector implementation gets substate as first argument, and rest args just compied.
Selector from combine gets entire state as first argument, and any rest args.
Also selector implementation gets entire state as last argument. It's same as in combine-section-reducer module.

Example

reducer for counter

const counter = (state = 0, action) => {
    switch (action.type) {
        case `ADD`:
            return state + action.payload;
        default:
            return state;
    }
}
export default counter;

selectors for counter

export const getCount = (state, minusCount) => state - minusCount;

combine

import {combineReducers} from 'redux';
import combineSelectors from 'combine-section-selectors';
import counter from './counter';
import * as fromCounter from './counter.selectors';

const reducer = combineReducers({
    counter,
});

const fromState = combineSelectors({
    counter: fromCounter,
});

const store = createStore(reducer);
store.dispatch({type: `ADD`, payload: 5});
fromState.getCount(store.getState(), 3); // returns 2 (5 in state minus 3 from argument)

Motivation and alternatives

Without such module you should always set path to entity in selector:

const getUser = (state, userId) => state.data.users.entities[userId];

which is awkward, because it makes this selector depending on where substate is connected to entire state.
Or even worse, pass path to substate on every usage of selector:

fromState.getUser(state.data.users, userId);