React Native common parts

http.js

const toJSON = r => r.json()

const checkStatus = (r) => {
  if (r.ok) return r

  return toJSON(r)
    .then((body) => {
      let error = new Error(r.statusText)
      error.body = body
      error.response = r
      throw error
    })
}

export const get = (url, options = {}) => {
  return fetch(url, options).then(checkStatus).then(toJSON)
}

export const post = (url, body, options = {}) => {
  options = {
    headers: {
      'Content-Type': 'application/json',
      'Accepts': 'application/json',
    },
    method: 'post',
    body: JSON.stringify(body),
    ...options,
  }
  return fetch(url, options).then(checkStatus).then(toJSON)
}

storage.js

import { AsyncStorage } from 'react-native'

const serialize = (value) => {
  return JSON.stringify(value)
}

const deserialize = (value) => {
  try {
    return JSON.parse(value)
  } catch (e) {
    return value
  }
}

export const getItem = (key) => {
  return AsyncStorage.getItem(key)
    .then(deserialize)
}

export const setItem = (key, value) => {
  return AsyncStorage.setItem(key, serialize(value))
}