Protected routes in frontend in Supabase - Mini Project: Build & Apply

Protected Routes in Frontend with Supabase

📖 Scenario: You are building a simple web app that shows some pages only to logged-in users. You will use Supabase for user authentication. Your app has a home page and a dashboard page. The dashboard page should be protected so only logged-in users can see it.

🎯 Goal: Build a frontend app with Supabase authentication that protects the dashboard route. If a user is not logged in, they should be redirected to the home page.

📋 What You'll Learn

Create a Supabase client instance

Check user authentication status

Create a protected route component

Redirect unauthenticated users to home page

💡 Why This Matters

🌍 Real World

Many web apps need to restrict access to certain pages based on user login status. This project shows how to do that simply with Supabase and React.

💼 Career

Understanding protected routes and authentication is essential for frontend developers working with cloud backends and user management.

1

Setup Supabase Client

Create a constant called supabase by calling createClient with the exact arguments 'https://xyzcompany.supabase.co' and 'public-anonymous-key'.

Supabase

# Create the Supabase client instance
# Your code here

Hint

Use createClient from Supabase with the given URL and key.

2

Check User Authentication Status

Create an async function called checkUser that calls supabase.auth.getUser() and stores the result in a constant called user.

Supabase

import { createClient } from '@supabase/supabase-js';

const supabase = createClient('https://xyzcompany.supabase.co', 'public-anonymous-key');

// Create async function checkUser
# Your code here

Hint

Use await supabase.auth.getUser() and extract user from the response.

3

Create Protected Route Component

Create a React functional component called ProtectedRoute that calls checkUser() inside a useEffect. If user is null, redirect to '/' using window.location.href.

Supabase

import { createClient } from '@supabase/supabase-js';
import React, { useEffect, useState } from 'react';

const supabase = createClient('https://xyzcompany.supabase.co', 'public-anonymous-key');

async function checkUser() {
    const { data: { user } } = await supabase.auth.getUser();
    return user;
}

// Create ProtectedRoute component
# Your code here

Hint

Use useState to hold user and useEffect to check user on mount. Redirect if no user.

4

Use ProtectedRoute to Wrap Dashboard

Wrap the <Dashboard /> component inside <ProtectedRoute> tags in the main app component.

Supabase

import { createClient } from '@supabase/supabase-js';
import React, { useEffect, useState } from 'react';

const supabase = createClient('https://xyzcompany.supabase.co', 'public-anonymous-key');

async function checkUser() {
    const { data: { user } } = await supabase.auth.getUser();
    return user;
}

function ProtectedRoute({ children }) {
    const [user, setUser] = useState(null);

    useEffect(() => {
        checkUser().then(currentUser => {
            if (!currentUser) {
                window.location.href = '/';
            } else {
                setUser(currentUser);
            }
        });
    }, []);

    if (!user) {
        return null;
    }

    return children;
}

function Dashboard() {
    return Dashboard Page;
}

function App() {
    return (
        
            Home Page
            {/* Wrap Dashboard with ProtectedRoute here */}
            # Your code here
        
    );
}

Hint

Use <ProtectedRoute><Dashboard /></ProtectedRoute> inside the App component.

Practice

1. What is the main purpose of protected routes in a frontend application using Supabase?

easy

A. To allow only logged-in users to access certain pages

B. To speed up page loading times

C. To store user data permanently

D. To change the app's theme automatically

Solution

1. Step 1: Understand what protected routes do

   Protected routes restrict access to certain pages so only authorized users can see them.

2. Step 2: Connect with Supabase session usage

   Supabase sessions help check if a user is logged in, enabling route protection.

3. Final Answer:

   To allow only logged-in users to access certain pages -> Option A

4. Quick Check:

   Protected routes = restrict access to logged-in users [OK]

Hint: Protected routes block access unless user is logged in [OK]

Common Mistakes:

• Thinking protected routes speed up loading
• Confusing route protection with data storage
• Assuming protected routes change app appearance

2. Which of the following is the correct way to check if a user is logged in using Supabase in frontend code?

easy

A. const user = supabase.auth.getUser()

B. const user = supabase.session()

C. const user = supabase.auth.session()

D. const user = supabase.auth.getSession()

Solution

1. Step 1: Identify Supabase method for session retrieval

   Supabase's current method to get session info is auth.getSession(), which returns user session data.

2. Step 2: Compare options with official API

   Options A, B, and C are outdated or incorrect method names; only getSession() is valid.

3. Final Answer:

   const user = supabase.auth.getSession() -> Option D

4. Quick Check:

   Use auth.getSession() to check login [OK]

Hint: Use supabase.auth.getSession() to get current user session [OK]

Common Mistakes:

• Using deprecated methods like auth.session()
• Calling supabase.session() which does not exist
• Confusing getUser() with getSession()

3. Given this React snippet using Supabase, what will happen if the user is not logged in?

const session = supabase.auth.getSession();
if (!session) {
  navigate('/login');
} else {
  showDashboard();
}

medium

A. The dashboard is shown regardless

B. An error is thrown because getSession() is async

C. The user is redirected to the login page

D. Nothing happens; the page stays the same

Solution

1. Step 1: Understand getSession() behavior

   supabase.auth.getSession() is an asynchronous function returning a Promise, so calling it without await assigns a Promise object to session, not session data.

2. Step 2: Analyze the code flow

   A Promise object is truthy, so if (!session) evaluates to false, and showDashboard() executes regardless of login status.

3. Final Answer:

   The dashboard is shown regardless -> Option A

4. Quick Check:

   Async getSession() without await returns truthy Promise [OK]

Hint: Remember to await async getSession() calls [OK]

Common Mistakes:

• Treating async getSession() as synchronous
• Assuming session is null if user not logged in
• Ignoring Promise returned by getSession()

4. You wrote this code to protect a route but it redirects even logged-in users to login:

const { data: session } = supabase.auth.getSession();
if (!session) {
  window.location.href = '/login';
}

What is the main issue?

medium

A. session is always truthy even if user is logged out

B. window.location.href cannot redirect pages

C. getSession() is asynchronous and must be awaited

D. You must use supabase.auth.getUser() instead

Solution

1. Step 1: Check getSession() usage

   supabase.auth.getSession() returns a Promise and must be awaited or handled asynchronously to get session data.

2. Step 2: Understand destructuring without await

   Destructuring data from a Promise without await results in undefined or incorrect values, so session is not properly checked.

3. Final Answer:

   getSession() is asynchronous and must be awaited -> Option C

4. Quick Check:

   Always await async getSession() calls [OK]

Hint: Always await async Supabase calls to get real data [OK]

Common Mistakes:

• Not awaiting async functions
• Thinking window.location.href can't redirect
• Using getUser() instead of getSession() incorrectly

5. You want to protect a React page so only logged-in users can see it. Which approach correctly implements this using Supabase's session and React hooks?

function ProtectedPage() {
  const [session, setSession] = React.useState(null);

  React.useEffect(() => {
    const getSession = async () => {
      const { data } = await supabase.auth.getSession();
      setSession(data.session);
      if (!data.session) {
        navigate('/login');
      }
    };
    getSession();
  }, []);

  if (!session) return <p>Loading...</p>;
  return <div>Welcome to protected content!</div>;
}

hard

A. The navigate call should be outside the async function

B. This code correctly protects the page by redirecting unauthenticated users

C. The code should call supabase.auth.getUser() instead of getSession()

D. The session state should be initialized with supabase.auth.getSession() synchronously

Solution

1. Step 1: Analyze async session retrieval in useEffect

   The code correctly uses an async function inside useEffect to get the session and update state.

2. Step 2: Check redirect logic for unauthenticated users

   If no session exists, the code calls navigate('/login') to redirect users, protecting the page.

3. Step 3: Confirm loading state handling

   While session is null, it shows a loading message, preventing content flash before redirect.

4. Final Answer:

   This code correctly protects the page by redirecting unauthenticated users -> Option B

5. Quick Check:

   Async session check + redirect = protected route [OK]

Hint: Use async useEffect with redirect on no session [OK]

Common Mistakes:

• Using getUser() instead of getSession() for session check
• Calling navigate outside async context incorrectly
• Initializing session state synchronously causing errors