next.js/examples/with-apollo-and-redux-saga/lib/clock/reducers.js

import { actionTypes } from './actions'

export const initialState = {
  lastUpdate: 0,
  light: false
}

function reducer(state = initialState, action) {
  switch (action.type) {
    case actionTypes.TICK_CLOCK:
      return {
        ...state,
        ...{ lastUpdate: action.lastUpdate, light: !!action.light }
      }

    default:
      return state
  }
}

export default reducer