Conditional routes in NextJS

Introduction

Conditional routes let your app show different pages or content based on rules like user login or role. This helps make your app smarter and safer.

Show a login page only if the user is not logged in.

Redirect users to a dashboard if they are already logged in.

Display admin pages only to users with admin rights.

Hide certain pages from visitors who don't have permission.

Change navigation links based on user status.

Syntax

NextJS

import { useRouter } from 'next/router';
import { useEffect } from 'react';

export default function Page() {
  const router = useRouter();
  const user = /* get user info, e.g. from context or state */;

  useEffect(() => {
    if (!user) {
      router.push('/login');
    }
  }, [user, router]);

  return <div>Protected Content</div>;
}

Use useRouter from Next.js to navigate programmatically.

Put your condition inside useEffect to run after the component loads.

Examples

Redirects to login if the user is not logged in.

NextJS

import { useRouter } from 'next/router';
import { useEffect } from 'react';

export default function Home() {
  const router = useRouter();
  const isLoggedIn = false;

  useEffect(() => {
    if (!isLoggedIn) {
      router.push('/login');
    }
  }, [isLoggedIn, router]);

  return <h1>Welcome Home</h1>;
}

Redirects non-admin users to a 'not authorized' page.

NextJS

import { useRouter } from 'next/router';
import { useEffect } from 'react';

export default function AdminPage() {
  const router = useRouter();
  const userRole = 'user';

  useEffect(() => {
    if (userRole !== 'admin') {
      router.push('/not-authorized');
    }
  }, [userRole, router]);

  return <div>Admin Content</div>;
}

Sample Program

This component waits for user info. If the user is not logged in, it redirects to login. Otherwise, it shows a welcome message.

NextJS

import { useRouter } from 'next/router';
import { useEffect, useState } from 'react';

export default function Dashboard() {
  const router = useRouter();
  const [user, setUser] = useState(null);

  // Simulate fetching user info
  useEffect(() => {
    setTimeout(() => {
      setUser({ name: 'Alice', loggedIn: true });
    }, 1000);
  }, []);

  useEffect(() => {
    if (user && !user.loggedIn) {
      router.push('/login');
    }
  }, [user, router]);

  if (!user) return <p>Loading user info...</p>;

  return <h1>Welcome to your dashboard, {user.name}!</h1>;
}

Important Notes

Always check user info or permissions before showing protected pages.

Use router.push() to change routes programmatically.

Remember to handle loading states while checking conditions.

Summary

Conditional routes help control who sees what in your app.

Use Next.js useRouter and useEffect to redirect based on conditions.

Always handle loading and permission checks carefully for good user experience.

Practice

1. What is the main purpose of conditional routes in Next.js?

easy

A. To create static pages only

B. To style pages differently

C. To fetch data from an API

D. To control access and redirect users based on conditions

Solution

1. Step 1: Understand conditional routes concept

   Conditional routes let you decide which users can see certain pages or redirect them elsewhere.

2. Step 2: Identify the purpose in Next.js

   Next.js uses conditional routes mainly to protect pages or redirect users based on login or roles.

3. Final Answer:

   To control access and redirect users based on conditions -> Option D

4. Quick Check:

   Conditional routes = control access [OK]

Hint: Think: Who should see this page? Redirect if no permission. [OK]

Common Mistakes:

• Confusing conditional routes with styling or data fetching
• Thinking conditional routes create static pages
• Believing conditional routes only fetch data

2. Which Next.js hook is commonly used to perform client-side redirects in conditional routes?

easy

A. useState

B. useEffect

C. useRouter

D. useContext

Solution

1. Step 1: Identify hooks for routing

   Next.js provides useRouter to access routing methods like push for redirects.

2. Step 2: Confirm redirect usage

   While useEffect runs side effects, useRouter is needed to actually change routes.

3. Final Answer:

   useRouter -> Option C

4. Quick Check:

   Redirects use useRouter [OK]

Hint: Redirects need router methods, so useRouter is key. [OK]

Common Mistakes:

• Using useState to redirect (it manages state only)
• Confusing useEffect as the hook that changes routes
• Thinking useContext handles routing

3. Given this Next.js component, what will happen if isLoggedIn is false?

import { useRouter } from 'next/router';
import { useEffect } from 'react';

export default function Dashboard() {
  const router = useRouter();
  const isLoggedIn = false;

  useEffect(() => {
    if (!isLoggedIn) {
      router.push('/login');
    }
  }, [isLoggedIn]);

  return <h1>Dashboard</h1>;
}

medium

A. The user is redirected to the /login page

B. The page reloads infinitely

C. The page shows an error

D. The user stays on the Dashboard page

Solution

1. Step 1: Analyze the useEffect condition

   The effect checks if isLoggedIn is false, then calls router.push('/login').

2. Step 2: Understand router.push behavior

   This causes a client-side redirect to the login page when not logged in.

3. Final Answer:

   The user is redirected to the /login page -> Option A

4. Quick Check:

   False login triggers redirect [OK]

Hint: False login triggers router.push to /login. [OK]

Common Mistakes:

• Thinking the user stays on Dashboard despite redirect
• Assuming an error occurs without redirect
• Believing infinite reload happens here

4. Identify the error in this Next.js conditional route code:

import { useRouter } from 'next/router';
import { useEffect } from 'react';

export default function Profile() {
  const router = useRouter();
  const isAuthorized = false;

  if (!isAuthorized) {
    router.push('/unauthorized');
  }

  return <h1>Profile</h1>;
}

medium

A. Calling router.push inside the component body causes an error

B. Missing dependency array in useEffect

C. useRouter is not imported correctly

D. The component returns invalid JSX

Solution

1. Step 1: Check where router.push is called

   router.push is called directly inside the component body, which runs on every render and is not allowed.

2. Step 2: Correct usage with useEffect

   Redirects should be inside useEffect to avoid infinite loops or errors.

3. Final Answer:

   Calling router.push inside the component body causes an error -> Option A

4. Quick Check:

   Redirects must be inside useEffect [OK]

Hint: Put router.push inside useEffect, not directly in component body. [OK]

Common Mistakes:

• Calling router.push directly in component body
• Ignoring useEffect for side effects
• Assuming missing import causes error here

5. You want to create a Next.js page that only logged-in users can access. If the user is not logged in, redirect them to '/login'. Which is the best approach?

1. Use useRouter and useEffect to check login and redirect client-side.
2. Use Next.js middleware to check authentication before rendering.
3. Render a loading state while checking login status.
4. Avoid rendering protected content until login is confirmed.

Which combination correctly applies conditional routing best practice?

hard

A. Only 1 and 2

B. All 1, 2, 3, and 4

C. Only 2 and 4

D. Only 1, 3, and 4

Solution

1. Step 1: Understand client-side and server-side checks

   Client-side redirect with useRouter/useEffect (1) is common, but middleware (2) adds server-side protection.

2. Step 2: Consider user experience

   Showing a loading state (3) and avoiding rendering protected content before login confirmation (4) improve UX and prevent flicker.

3. Step 3: Combine all for best practice

   Using all four ensures secure, smooth conditional routing in Next.js.

4. Final Answer:

   All 1, 2, 3, and 4 -> Option B

5. Quick Check:

   Best practice = all steps combined [OK]

Hint: Combine client, server checks and loading states for best routing. [OK]

Common Mistakes:

• Relying only on client-side redirects
• Skipping loading states causing flicker
• Ignoring server-side middleware protection