Atomic file storage engine for redux-storage

redux-storage-engine-file.js

import fs from 'fs';
import tmp from 'tmp';

export default (filename) => ({
  load() {
    return new Promise((resolve, reject) => {
      fs.readFile(filename, (err, contents) => {
        if (err) {
          if (err.code === 'ENOENT') {
            resolve({})
          } else {
            reject(err)
          }
        } else {
          resolve(JSON.parse(contents))
        }
      })
    })
  },

  save(state) {
    return new Promise((resolve, reject) => {
      tmp.file((err, tmpfilename) => {
        if (err) {
          return reject(err)
        }
        fs.writeFile(tmpfilename, JSON.stringify(state), (err) => {
          if (err) {
            return reject(err)
          }
          fs.rename(tmpfilename, filename, (err) => {
            if (err) {
              return reject(err)
            }
            resolve()
          })
        })
      })
    })
  }
})