How to check if the user is logged in to Firebase

In applications integrated with Firebase, verifying whether a user is logged in is necessary to ensure a seamless and secure user experience. By confirming the user’s login status, developers can tailor the application’s interface and functionality accordingly, offering personalized content and features to authenticated users while guiding non-authenticated users toward the login or signup flow. Moreover, verifying login status is essential for enforcing access control, safeguarding sensitive data, and managing authentication-related workflows effectively. In this Answer, we’ll learn to check whether a user is logged in to Firebase.

Note: We'll use React Native to check whether a user is logged in to Firebase. However, the concepts learned are easily transferable over other programming languages and frameworks as well.

Follow the steps outlined below to check whether a user is logged in to Firebase.

Create a Firebase project

Firstly, ensure that you have a Firebase project set up. It serves as the foundation for user authentication functionalities within the application. Firebase provides the necessary services to manage user authentication securely, allowing us to integrate login functionalities seamlessly into the application.

Secondly, ensure that you have the Firebase credentials for the above-mentioned Firebase project. The Firebase credentials contain important information, such as the Firebase project’s API key, authentication domain, and database URL. These credentials are essential for establishing a secure connection between the application and the Firebase backend services. They authenticate the application with Firebase, enabling features like user authentication, data storage, and real-time updates.

Note: It's crucial to keep the Firebase credentials confidential to prevent unauthorized access to the Firebase resources.

Follow the “How to create Cloud Firestore database for React Native” Answer to learn how to create a Firebase project and obtain Firebase credentials. You only have to follow the steps mentioned under the headings “Create a Firebase project” and “Obtain credentials for the Firebase configuration file.”

Enable Firebase authentication

Next, we need to enable Firebase authentication. Firebase authentication is a service provided by Firebase that handles user authentication in applications. It allows users to sign up, sign in, and manage their authentication state securely. For this Answer, we’ll use “Email/Password” as the sign-in method. Follow the steps outlined below to enable Firebase authentication within the Firebase project.

Add Firebase credentials to the Firebase configuration file

Once the above steps have been completed, we need to add the Firebase credentials to the Firebase configuration file. Adding Firebase credentials to the configuration file allows the application to securely authenticate and communicate with Firebase services. This file serves as a crucial link between the application and Firebase, enabling features such as user authentication, database access, and cloud functions. The code snippet below shows what the Firebase configuration file looks like in React Native.

In the code snippet above:

• Line 1: We import the initializeApp function from the firebase/app module. This function is used to initialize the Firebase application with the provided Firebase credentials.

• Line 2: We import initializeAuth, getReactNativePersistence, and browserLocalPersistencefrom from the firebase/auth module. These are used to initialize Firebase authentication and set the persistence method for the authentication state.

• Line 3: We import ReactNativeAsyncStorage from @react-native-async-storage/async-storage. This import is used as a persistence layer for the authentication state in React Native applications.

• Line 4: We import Platform from react-native. This module is used to detect the current platform.

• Lines 6–14: We set up the Firebase configuration object with the Firebase credentials that you obtained previously. At this stage, you do not need to add the Firebase credentials. You’ll add them toward the end of this Answer within the “Coding playground” section.

• Line 16: We initialize the Firebase application with the provided Firebase configuration/credentials.

• Lines 18–24: We initialize the Firebase authentication based on the platform using appropriate persistence settings.

• Line 26: We export the auth object to be used with other parts of the application. The auth object will be used for handling user authentication in the React Native application.

Write the login method

To check if the user is logged in to Firebase, we first need to write a method to allow the user to log in. The code snippet below shows what the login method will look like in React Native.

In the code snippet above:

• Lines 1–3: We import the required libraries and methods.

• Line 5: We use the useState Hook to initialize a state variable named email. We set the default value to an empty string. This variable will be used to keep track of the user’s email.

• Line 6: We use the useState Hook to initialize a state variable named password. We set the default value to an empty string. This variable will be used to keep track of the user's password.

• Lines 8–24: We define a function named login. This function will be used to log the user into the application. Within this function:

  • Lines 9–12: If the email or password state variables are an empty string, we display an appropriate error message and return from the function.

  • Lines 14: We use the signInWithEmailAndPassword method from the firebase/auth module to sign the user into the application. We pass the auth object and the email and password state variables as parameters to the function.

  • Lines 15: If the user is signed in successfully, we display an appropriate success message.

  • Lines 17–22: If there are any errors using the sign-in process, we display the appropriate error messages.

Write the checkLoginStatus and logout methods

Next, we need to write the checkLoginStatus and logout methods. The checkLoginStatus method will be used to check if the user is logged in to Firebase. On the other hand, the logout method will be used to log the user out of the application. Once the user has been logged out, we can again use the checkLoginStatus method to verify that the user has indeed been logged out of the application. The code snippet below shows what the checkLoginStatus and logout methods will look like in React Native.

In the code snippet above:

• Lines 1–8: We define a function named checkLoginStatus. Within the function, we check the auth.currentUser. If it is null, we display an appropriate error message. Otherwise, we log auth.currentUser onto the console and display an appropriate success message. Note that auth.currentUser is an object containing all the information related to the currently logged-in user, such as the email and displayName.

• Lines 10–20: We define a function named logout. Within this function, we check the auth.currentUser. If it is null, we display an appropriate message that no user is currently logged in. Otherwise, we use the signOut() method from the auth object to log the user out of the application. We then reset the state variables and display an appropriate success message.

Coding playground

Utilize the coding playground below to see the above concepts in action. Before executing the code using the “Run” button, make sure to add your Firebase credentials inside the firebaseConfig.js file. Once the code has been executed, click the link next to the text “Your app can be found at:” to open the application. The text is located at the bottom of the coding playground below.

In conclusion, by following the outlined steps, you can effectively verify whether a user is logged in to Firebase. These steps provide a clear path for implementing user authentication checks within applications, ensuring seamless user experiences and enhanced security measures.