Chain of dependency inversion

dependency-inversion-chain.js

/* json.js */

export default function ({ readFileAsync, writeFileAsync }) {
  return {
    readJsonFile(fileName) {
      return readFileAsync(`${fileName}.json`).then(JSON.parse) 
    },
    writeJsonFile(filePath, fileContent) {
      return writeFileAsync(filePath, JSON.stringify(fileContent)) 
    }
  }
}

/* content.js */

export default function ({ readJsonFile, writeJsonFile }) {
  return {
     getContent(contentName) {
      // business logic goes here.
      return readJsonFile(contentName)
     },
     writeContent(contentName, contentText) {
      // business logic goes here
      return writeJsonFile(contentName, contentText) 
     }
  }
}

/* index.js where the app starts */

import fs from 'fs-extra-promise'
import jsonInterface from './json'
import contentInterface from './content'

const json = jsonInterface(fs)
const content = contentInterface(json)

// content can be used by an http server
// or just exported if this is a library
export default content