Read async from lowdb

lowdb-async-store.js

import { exists, readFile, writeFile } from 'graceful-fs';
import { parse } from 'json-parse-helpfulerror';
import fileAsync from 'lowdb/lib/file-async';


/**
 * Custom storage for `lowdb`, b/c we want to have read AND
 * write to be async. This will make the API more easy to use.
 */
const storage = {
  read: file => {
    return new Promise((resolve, reject) => {
      // Asynchronously read database and parse JSON to `object`.
      function readDatabase () {
        readFile(file, 'utf8', (err, data) => {
          if (err) { return reject(err); }

          try {
            resolve(parse(data.trim() || '{}'));
          }
          catch (e) {
            if (e instanceof SyntaxError) {
              e.message = `Malformed JSON in file: ${file}\n${e.message}`;
            }
            reject(e);
          }
        });
      }

      // Asynchronously create an empty database (JSON file).
      function initEmptyDatabase () {
        writeFile(file, '{}', err => {
          if (err) { return reject(err); }
          resolve({});
        });
      }

      // Depending if the file exists, we read it or create an empty
      // database.
      exists(file, result => result ? readDatabase() : initEmptyDatabase());
    });
  },
  write: fileAsync.write
};

export default storage;

NOTE: This forces you to always do db.read/db.write, but the API still is not really async/promise-based. E.g. getState is still synchronous ...