Enable createMigrate to handle async migrations rt2zz#866

docs/migrations.md

@@ -13,7 +13,19 @@ const migrations = {
  device: undefined 
  }
  },
- 1: (state) => {
+ // You can use also `async () => {}` function
+ // For example to move users to other storage
+ 1: async ({ users, ...state }) => {
+ try {
+ await insertToOtherStorage(users)
+
+ return state
+ } catch (e) {
+ // Don't forget about exceptions
+ return state
+ }
+ },
+ 2: (state) => {
  // migration to keep only device state
  return {
  device: state.device

src/createMigrate.js

@@ -42,15 +42,16 @@ export default function createMigrate(
  if (process.env.NODE_ENV !== 'production' && debug)
  console.log('redux-persist: migrationKeys', migrationKeys)
  try {
- let migratedState = migrationKeys.reduce((state, versionKey) => {
+ return migrationKeys.reduce((promiseState, versionKey) => {
  if (process.env.NODE_ENV !== 'production' && debug)
  console.log(
  'redux-persist: running migration for versionKey',
  versionKey
  )
- return migrations[versionKey](state)
- }, state)
- return Promise.resolve(migratedState)
+ return promiseState.then(state =>
+ Promise.resolve(migrations[versionKey](state))
+ )
+ }, Promise.resolve(state))
  } catch (err) {
  return Promise.reject(err)
  }