Apps currently using any namespaced Firebase Web API, from the compat
libraries
back through version 8 or earlier, should consider
migrating to the modular API using the instructions in this guide.
This guide assumes that you are familiar with the namespaced API and that you will take advantage of a module bundler such as webpack or Rollup for upgrading and ongoing modular app development.
Using a module bundler in your development environment is strongly recommended. If you don't use one, you won't be able to take advantage of the modular API's main benefits in reduced app size. You'll need npm or yarn to install the SDK.
The upgrade steps in this guide will be based around an imaginary web app that uses the Authentication and Cloud Firestore SDKs. By working through the examples, you can master the concepts and practical steps required to upgrade all supported Firebase Web SDKs.
About the namespaced (compat
) libraries
There are two types of libraries available for the Firebase Web SDK:
- Modular - a new API surface designed to facilitate tree-shaking (removal of unused code) to make your web app as small and fast as possible.
- Namespaced (
compat
) - a familiar API surface which is fully compatible with the earlier versions of the SDK, allowing you to upgrade without changing all of your Firebase code at once. Compat libraries have little to no size or performance advantages over their namespaced counterparts.
This guide assumes that you will take advantage of the compat libraries to facilitate your upgrade. These libraries allow you to continue using namespaced code alongside code refactored for the modular API. This means you can compile and debug your app more easily as you work through the upgrade process.
For apps with a very small exposure to the Firebase Web SDK—for example, an app that makes only a simple call to the Authentication APIs—it may be practical to refactor older namespaced code without using the compat libraries. If you are upgrading such an app, you can follow the instructions in this guide for "the modular API" without using the compat libraries.
About the upgrade process
Each step of the upgrade process is scoped so that you can finish editing the source for your app and then compile and run it without breakage. In summary, here's what you'll do to upgrade an app:
- Add the modular libraries and the compat libraries to your app.
- Update import statements in your code to compat.
- Refactor code for a single product (for example, Authentication) to the modular style.
- Optional: at this point, remove the Authentication compat library and compat code for Authentication in order to realize the app size benefit for Authentication before continuing.
- Refactor functions for each product (for example, Cloud Firestore, FCM, etc.) to the modular style, compiling and testing until all areas are complete.
- Update initialization code to the modular style.
- Remove all remaining compat statements and compat code from your app.
Get the latest version of the SDK
To get started, get the modular libraries and compat libraries using npm:
npm i firebase@10.14.0 # OR yarn add firebase@10.14.0
Update imports to compat
In order to keep your code functioning after updating your dependencies, change your import statements to use the "compat" version of each import. For example:
Before: version 8 or earlier
import firebase from 'firebase/app';
import 'firebase/auth';
import 'firebase/firestore';
After: compat
// compat packages are API compatible with namespaced code
import firebase from 'firebase/compat/app';
import 'firebase/compat/auth';
import 'firebase/compat/firestore';
Refactor to the modular style
While the namespaced APIs are based on a dot-chained namespace and service
pattern, the modular approach means that your code will be organized
principally around functions. In the modular API, the firebase/app
package and
other packages do not return a comprehensive export that contains all the
methods from the package. Instead, the packages export individual functions.
In the modular API, services are passed as the first argument, and the function then uses the details of the service to do the rest. Let's examine how this works in two examples that refactor calls to the Authentication and Cloud Firestore APIs.
Example 1: refactoring an Authentication function
Before: compat
The compat code is identical to the namespaced code, but the imports have changed.
import firebase from "firebase/compat/app";
import "firebase/compat/auth";
const auth = firebase.auth();
auth.onAuthStateChanged(user => {
// Check for user status
});
After: modular
The getAuth
function takes firebaseApp
as its first parameter.
The onAuthStateChanged
function is not chained from the auth
instance as it would be
in the namespaced API; instead, it's a free
function which takes auth
as its first parameter.
import { getAuth, onAuthStateChanged } from "firebase/auth";
const auth = getAuth(firebaseApp);
onAuthStateChanged(auth, user => {
// Check for user status
});
Update handling of Auth method getRedirectResult
The modular API introduces a breaking change in getRedirectResult
. When no redirect operation is called, the modular API returns null
as opposed to the namespaced API, which returned a UserCredential
with a null
user.
Before: compat
const result = await auth.getRedirectResult()
if (result.user === null && result.credential === null) {
return null;
}
return result;
After: modular
const result = await getRedirectResult(auth);
// Provider of the access token could be Facebook, Github, etc.
if (result === null || provider.credentialFromResult(result) === null) {
return null;
}
return result;
Example 2: refactoring a Cloud Firestore function
Before: compat
import "firebase/compat/firestore"
const db = firebase.firestore();
db.collection("cities").where("capital", "==", true)
.get()
.then((querySnapshot) => {
querySnapshot.forEach((doc) => {
// doc.data() is never undefined for query doc snapshots
console.log(doc.id, " => ", doc.data());
});
})
.catch((error) => {
console.log("Error getting documents: ", error);
});
After: modular
The getFirestore
function takes firebaseApp
as its first parameter, which
was returned from initializeApp
in an earlier example. Note how the
code to form a query is very different in the modular API; there is no chaining, and
methods such as query
or where
are now exposed as free functions.
import { getFirestore, collection, query, where, getDocs } from "firebase/firestore";
const db = getFirestore(firebaseApp);
const q = query(collection(db, "cities"), where("capital", "==", true));
const querySnapshot = await getDocs(q);
querySnapshot.forEach((doc) => {
// doc.data() is never undefined for query doc snapshots
console.log(doc.id, " => ", doc.data());
});
Update references to Firestore DocumentSnapshot.exists
The modular API introduces a breaking change in which the property
firestore.DocumentSnapshot.exists
has been changed to a method. The
functionality is essentially the same (testing whether a document exists)
but you must refactor your code to use the newer method as shown:
Before:compat
if (snapshot.exists) {
console.log("the document exists");
}
After: modular
if (snapshot.exists()) {
console.log("the document exists");
}
Example 3: combining namespaced and modular code styles
Using the compat libraries during upgrade allows you to continue using namespaced code alongside code refactored for the modular API. This means you can keep existing namespaced code for Cloud Firestore while you refactor Authentication or other Firebase SDK code to the modular style, and still successfully compile your app with both code styles. The same is true for namespaced and modular API code within a product such as Cloud Firestore; new and old code styles can coexist, as long as you are importing the compat packages:
import firebase from 'firebase/compat/app';
import 'firebase/compat/firestore';
import { getDoc } from 'firebase/firestore'
const docRef = firebase.firestore().doc();
getDoc(docRef);
Keep in mind that, although your app will compile, you won't get the app size benefits of the modular code until you fully remove the compat statements and code from your app.
Update initialization code
Update your app's initialization code to use modular syntax. It is
important to update this code after you have completed refactoring all the
code in your app; this is because firebase.initializeApp()
initializes global
state for both the compat and modular APIs, whereas the modular
initializeApp()
function initializes only the state for modular.
Before: compat
import firebase from "firebase/compat/app"
firebase.initializeApp({ /* config */ });
After: modular
import { initializeApp } from "firebase/app"
const firebaseApp = initializeApp({ /* config */ });
Remove compat code
To realize the size benefits of the modular API, you should eventually
convert all invocations to the modular style shown above and remove all of the
import "firebase/compat/*
statements from your code. When you are done, there
should be no more references to the firebase.*
global namespace or any other
code in the namespaced API style.
Using the compat library from the window
The modular API is optimized to work with modules rather than the browser's
window
object. Previous versions of the library allowed the loading and
management of Firebase by using the window.firebase
namespace. This is not
recommended going forward as it does not allow for unused code elimination.
However, the compat version of the JavaScript SDK does work with the window
for developers who prefer not to immediately begin the modular upgrade path.
<script src="https://www.gstatic.com/firebasejs/10.14.0/firebase-app-compat.js"></script>
<script src="https://www.gstatic.com/firebasejs/10.14.0/firebase-firestore-compat.js"></script>
<script src="https://www.gstatic.com/firebasejs/10.14.0/firebase-auth-compat.js"></script>
<script>
const firebaseApp = firebase.initializeApp({ /* Firebase config */ });
const db = firebaseApp.firestore();
const auth = firebaseApp.auth();
</script>
The compatibility library uses modular code under the hood and provides it with the same API as the namespaced API; this means you can refer to the namespaced API reference and namespaced code snippets for details. This method is not recommended for long term use, but as a start to upgrade to the fully modular library.
Benefits and limitations of the modular SDK
The fully modularized SDK has these advantages over earlier versions:
- The modular SDK enables a dramatically reduced app size. It adopts the modern JavaScript Module format, allowing for "tree shaking" practices in which you import only the artifacts your app needs. Depending on your app, tree-shaking with the modular SDK can result in 80% less kilobytes than a comparable app built using the namespaced API.
- The modular SDK will continue to benefit from ongoing feature development, while the namespaced API will not.