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Firebase Auth Migrator

A JavaScript code sample for migrating logged in users from a legacy Firebase SDK to the new Firebase SDK.


Before using this code, you must add the Firebase JavaScript SDK to your page.

Getting Started

  1. Include migrate.js in your page.
  2. After you call firebase.initializeApp to initialize the Firebase SDK, call migrate to log in any user who was previously logged in with the legacy SDK.
firebase.authMigrator().migrate().then(function(user) {
  if (!user) {
    // No user was logged in.
  // user is logged in.
}).catch(function(error) {
  // There was an error.
  1. Whenever you log in a user, call clearLegacyAuth. This is a precaution to make sure that a user from a legacy SDK never overrides a newer log in.
firebase.auth().onAuthStateChanged(function(user) {
  if (user) {


If you've found an error in this sample, please file an issue:

Patches are encouraged, and may be submitted by forking this project and submitting a pull request through GitHub.


Copyright 2016 Google, Inc.

Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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