Sample reducer

reducer.js

const initialState = {
  token:: null,
  tokenIsExpired: false,
  errors: [],
  profile:null,
  loading: false
}

export default function auth(state = initialState, action) {
  switch(action.type) {
  case 'LOGIN_REQUEST':
    return {
      ...state,
      errors: errors(state.errors, action),
      loading: loading(state.loading, action)
    }
  case 'LOGIN_SUCCESS':
    return {
      ...state,
      token: token(state.token, action),
      errors: errors(state.errors, action),
      tokenIsExpired: tokenIsExpired(state.tokenIsExpired, action),
      loading: loading(state.loading, action)
    }
  case 'LOGIN_FAILURE':
    return {
      ...state,
      token: token(state.token, action),
      errors: errors(state.errors, action),
      tokenIsExpired: tokenIsExpired(state.tokenIsExpired, action),
      loading: loading(state.loading, action)
    }
  case 'LOGOUT_SUCCESS':
    return {
      ...state,
      token: token(state.token, action),
      tokenIsExpired: tokenIsExpired(state.tokenIsExpired, action),
      profile: profile(state.profile, action)
    }
  case 'SESSION_EXPIRED':
    return {
      ...state,
      tokenIsExpired: tokenIsExpired(state.tokenIsExpired, action)
    }
  case 'PROFILE_REQUEST':
    return {
      ...state,
      loading: loading(state.loading, action)
    }
  case 'PROFILE_SUCCESS':
    return {
      ...state,
      profile: profile(state.profile, action),
      loading: loading(state.profile, action)
    }
  default:
    return state
  }
}

function token(state, action) {
  switch(action.type) {
  case 'LOGIN_SUCCESS':
    return action.payload.token
  case 'LOGOUT_SUCCESS':
  case 'LOGIN_FAILURE':
    return null
  default:
    return state
  }
}

function errors(state, action) {
  switch(action.type) {
  case 'LOGIN_REQUEST':
  case 'LOGIN_SUCCESS':
    return []
  case 'LOGIN_FAILURE':
    return action.payload.errors
  default:
    return state
  }
}

function tokenIsExpired(state, action) {
  switch(action.type) {
  case 'LOGIN_SUCCESS':
  case 'LOGIN_FAILURE':
  case 'LOGOUT_SUCCESS':
    return false
  case 'SESSION_EXPIRED':
    return true
  default:
    return state
  }
}

function loading(state, action) {
  switch(action.type) {
  case 'LOGIN_REQUEST':
  case 'PROFILE_REQUEST':
    return true
  case 'LOGIN_FAILURE':
  case 'LOGIN_SUCCESS':
  case 'PROFILE_SUCCESS':
    return false
  default:
    return state
  }
}

function profile(state, action) {
  switch(action.type) {
  case 'LOGOUT_SUCCESS':
    return null
  case 'PROFILE_SUCCESS':
    return action.payload.profile
  default:
    return state
  }
}