Web extension: use for updating storage version. credit to @ettoolong

loadPreference.js

const loadPreference = async defaultPreference => {
  let results = await browser.storage.sync.get()

  if ((typeof results.length === 'number') && (results.length > 0)) {
    results = results[0]
  }

  if (!results.version) {
    await browser.storage.sync.set(defaultPreference)
    return defaultPreference
  }

  if (results.version === defaultPreference.version) return results

  let updateKeys = Object.keys(defaultPreference).filter( key => results[key] === undefined)
  if (updateKeys.length === 0) return defaultPreference;

  let update = updateKeys.reduce( (obj, key) => ({
    ...obj,
    key: defaultPreference[key]
  }), {})
  await browser.storage.sync.set(update)
  return {
    ...results,
    ...update
  }
}