Supabase: Get User ID With Client-Side Code

Oct 23, 2025 by Jhon Lennon 44 views

Hey guys! Ever needed to grab a user's ID when working with Supabase on the client-side? It's a common task, and I'm here to walk you through it. We'll cover everything from setting up your Supabase client to securely retrieving that user ID. Let's dive in!

Setting Up Your Supabase Client

Before we get started, you'll need to make sure your Supabase client is properly set up in your project. This involves initializing the client with your Supabase URL and anon key. Here’s a quick rundown:

Install the Supabase Client Library:

If you haven't already, add the Supabase client library to your project using npm or yarn.
```
npm install @supabase/supabase-js
# or
yarn add @supabase/supabase-js
```
Initialize the Supabase Client:

In your JavaScript file, import the createClient function and initialize the client with your Supabase URL and anon key. You can find these keys in your Supabase project settings under the 'API' section. Make sure to keep your anon key safe and avoid exposing your service_role key on the client-side.
```
import { createClient } from '@supabase/supabase-js';

const supabaseUrl = 'YOUR_SUPABASE_URL';
const supabaseAnonKey = 'YOUR_SUPABASE_ANON_KEY';

const supabase = createClient(supabaseUrl, supabaseAnonKey);
```
Make sure to replace 'YOUR_SUPABASE_URL' and 'YOUR_SUPABASE_ANON_KEY' with your actual Supabase URL and anon key.
Securing Your Keys:

For those of you working in a browser environment, consider using environment variables to manage your Supabase URL and anon key. This can help prevent accidental exposure of your keys in your codebase. Tools like dotenv (for local development) or environment variables in your hosting platform (like Netlify or Vercel) can be super helpful. For example, in a React app, you might use process.env.REACT_APP_SUPABASE_URL and process.env.REACT_APP_SUPABASE_ANON_KEY.
```
const supabaseUrl = process.env.REACT_APP_SUPABASE_URL;
const supabaseAnonKey = process.env.REACT_APP_SUPABASE_ANON_KEY;

const supabase = createClient(supabaseUrl, supabaseAnonKey);
```

With your Supabase client initialized, you're ready to start interacting with your Supabase database and, more importantly, grab that user ID.

Retrieving the User ID

Okay, now for the juicy part: getting the user ID. Supabase makes this pretty straightforward. Here’s how you can do it:

Accessing the Auth Object:

Supabase provides an auth object on the client that contains all the authentication-related methods and data. You can access the current user session through this object.
```
const session = supabase.auth.getSession();
```
Getting the Current User:

From the session, you can get the current user object. This object contains the user's ID, email, and other relevant information.
```
const user = session?.data?.session?.user;
```
Extracting the User ID:

Once you have the user object, you can extract the user ID using the id property.
```
const userId = user?.id;
console.log('User ID:', userId);
```
Here's the complete code snippet:
```
async function getUserId() {
  const { data: { session } } = await supabase.auth.getSession()

  const user = session?.user
  const userId = user?.id;
  console.log('User ID:', userId);
  return userId; // Return the user ID to use it elsewhere
}

getUserId();
```
Important Considerations:
- Asynchronous Nature: Remember that supabase.auth.getSession() is an asynchronous function, so you'll need to use await or .then() to handle the promise. Wrapping it in an async function makes it easier to work with.
- Session Management: Ensure that you have proper session management in place. The user needs to be authenticated and have an active session for this to work. Supabase handles session management automatically, but you should be aware of how sessions are created and maintained.
- Null Checks: Always perform null checks on the session and user objects before accessing their properties. This prevents errors when the user is not authenticated or the session is not available. Use the optional chaining operator (?.) to safely access nested properties.

Real-World Examples

Let's make this even more practical with some real-world examples of how you might use the user ID in your application.

Fetching User-Specific Data:

One of the most common use cases is fetching data that belongs to a specific user. For example, you might want to retrieve a list of tasks or projects associated with the logged-in user.
```
async function fetchUserTasks(userId) {
  const { data, error } = await supabase
    .from('tasks')
    .select('*')
    .eq('user_id', userId);

  if (error) {
    console.error('Error fetching tasks:', error);
    return [];
  }

  console.log('User tasks:', data);
  return data;
}

const userId = await getUserId();
if (userId) {
  fetchUserTasks(userId);
}
```
In this example, we're using the user_id to filter the tasks and only retrieve the ones that belong to the current user. Make sure you have a user_id column in your tasks table that references the users table.

Displaying User Information:

You might want to display the user's name, email, or other information on their profile page. You can use the user ID to fetch the user's profile from your database.

async function fetchUserProfile(userId) {
  const { data, error } = await supabase
    .from('profiles')
    .select('*')
    .eq('user_id', userId)
    .single();

  if (error) {
    console.error('Error fetching profile:', error);
    return null;
  }

  console.log('User profile:', data);
  return data;
}

const userId = await getUserId();
if (userId) {
  fetchUserProfile(userId);
}

Here, we're fetching the user's profile from a profiles table. The .single() method is used to ensure that we only retrieve one record. Again, ensure that your profiles table has a user_id column.

Implementing Role-Based Access Control (RBAC):

User IDs are crucial for implementing RBAC. You can check the user's role or permissions based on their ID and restrict access to certain features or data.

async function checkUserRole(userId) {
  const { data, error } = await supabase
    .from('user_roles')
    .select('role')
    .eq('user_id', userId)
    .single();

  if (error) {
    console.error('Error fetching user role:', error);
    return null;
  }

  console.log('User role:', data?.role);
  return data?.role;
}

async function grantAccess() {
  const userId = await getUserId();
  const role = await checkUserRole(userId);

  if (role === 'admin') {
    console.log('Access granted: Admin user');
    // Grant admin access
  } else {
    console.log('Access denied: Insufficient privileges');
    // Deny access
  }
}

grantAccess(); ```

In this example, we're fetching the user's role from a `user_roles` table and granting or denying access based on their role. This is a simplified example, but it illustrates the basic idea.

Handling Authentication State Changes

It’s important to handle authentication state changes in your application. Supabase provides a way to listen for authentication events and update your UI accordingly. This ensures that your application stays in sync with the user’s authentication status.

Listening for Auth State Changes:

You can use the supabase.auth.onAuthStateChange() method to listen for authentication events. This method is called whenever the user signs in, signs out, or their session is refreshed.

supabase.auth.onAuthStateChange((event, session) => {
  if (event === 'SIGNED_IN') {
    console.log('User signed in:', session?.user);
    // Update UI for signed-in state
  } else if (event === 'SIGNED_OUT') {
    console.log('User signed out');
    // Update UI for signed-out state
  } else if (event === 'PASSWORD_RECOVERY') {
      console.log('Password recovery email sent');
      // Handle password recovery event
  }
});

The event parameter indicates the type of authentication event, and the session parameter contains the user's session data. You can use this information to update your UI and perform other actions.

Updating the UI:

When the authentication state changes, you should update your UI to reflect the new state. For example, you might want to show a different set of navigation links or display a welcome message for signed-in users.

supabase.auth.onAuthStateChange((event, session) => {
  const user = session?.user;

  if (event === 'SIGNED_IN') {
    console.log('User signed in:', user);
    // Show welcome message
    document.getElementById('welcome-message').textContent = `Welcome, ${user.email}!`;
    // Show user-specific content
    document.getElementById('user-content').style.display = 'block';
  } else if (event === 'SIGNED_OUT') {
    console.log('User signed out');
    // Hide welcome message
    document.getElementById('welcome-message').textContent = '';
    // Hide user-specific content
    document.getElementById('user-content').style.display = 'none';
  }
});

In this example, we're updating the text content of a welcome-message element and showing or hiding a user-content element based on the authentication state. Make sure you have these elements in your HTML.

Security Considerations

Security is paramount when dealing with user data. Here are some best practices to keep in mind:

Never Expose Your service_role Key:

The service_role key has full access to your Supabase database and should never be exposed on the client-side. Use it only in your backend code or serverless functions.
Implement Row Level Security (RLS):

RLS allows you to define fine-grained access control policies at the database level. This ensures that users can only access the data they are authorized to access.
Sanitize User Input:

Always sanitize user input to prevent SQL injection attacks. Use parameterized queries or prepared statements to escape user input.
Use HTTPS:

Always use HTTPS to encrypt the communication between your client and server. This protects user data from being intercepted.

Conclusion

So there you have it, folks! Grabbing the user ID with Supabase on the client-side is super easy once you know the steps. Remember to set up your client correctly, handle those promises, and always keep security in mind. Now go build something awesome! Happy coding! Remember always to handle authentication state changes.