res.redirect for redirections in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when res.redirect is called with a relative URL?

Consider this Express route handler:

app.get('/old-page', (req, res) => {
  res.redirect('/new-page');
});

What will the browser do when a user visits /old-page?

Express

app.get('/old-page', (req, res) => {
  res.redirect('/new-page');
});

A The browser will navigate to 'http://new-page' as a full URL.

B The browser will stay on '/old-page' and display the content of '/new-page' without changing the URL.

C The browser will throw an error because the URL is relative.

D The browser will navigate to the absolute path '/new-page' on the same domain.

💡 Hint

Think about how relative URLs starting with '/' behave in web browsers.

When res.redirect is called with a URL starting with '/', it tells the browser to go to that path on the current domain. So the browser changes the URL to '/new-page' and loads that page.

📝 Syntax

intermediate

Which res.redirect usage is syntactically correct?

Which of the following Express code snippets correctly uses res.redirect to redirect to 'https://example.com'?

A res.redirect('https://example.com');

B res.redirect('301', 'https://example.com');

C res.redirect(301, 'https://example.com');

D res.redirect(redirectUrl = 'https://example.com');

💡 Hint

Check the official Express documentation for res.redirect method signatures.

The correct syntax to specify a status code and URL is res.redirect(statusCode, url). The status code must be a number, not a string. Option C uses 301 as a number, so it is correct.

🔧 Debug

advanced

Why does this code throw a server error?

Look at this Express route:

app.get('/start', (req, res) => {
  res.redirect('/middle');
  res.send('Done');
});

Why does this code cause a server-side error?

Express

app.get('/start', (req, res) => {
  res.redirect('/middle');
  res.send('Done');
});

A Calling res.send after res.redirect causes an error because the response is already sent.

B res.redirect does not send a response, so res.send is needed to complete it.

C Express requires next() to be called after res.redirect to complete the redirect.

D The redirect URL '/middle' is invalid and causes the redirect to fail silently.

💡 Hint

Think about what happens when you try to send two responses for one request.

Once res.redirect sends a response, calling res.send again causes an error because the response is already finished.

❓ state_output

advanced

What is the HTTP status code sent by default with res.redirect?

Given this Express code:

app.get('/go', (req, res) => {
  res.redirect('/target');
});

What HTTP status code will the client receive?

Express

app.get('/go', (req, res) => {
  res.redirect('/target');
});

A 302 (Found)

B 308 (Permanent Redirect)

C 307 (Temporary Redirect)

D 301 (Moved Permanently)

💡 Hint

Check the Express documentation for the default redirect status code.

By default, res.redirect sends a 302 status code, which means the resource is temporarily found at a new location.

🧠 Conceptual

expert

How does res.redirect handle absolute URLs with different domains?

If you use res.redirect('https://otherdomain.com/page') in Express, what happens in the browser?

A Express blocks redirects to external domains for security and throws an error.

B The browser navigates to the full URL 'https://otherdomain.com/page' on a different domain.

C The browser treats it as a relative path and navigates to '/https://otherdomain.com/page' on the current domain.

D The redirect is ignored and the original page remains loaded.

💡 Hint

Think about how browsers handle full URLs in HTTP redirects.

When res.redirect is given a full URL with a different domain, it sends a redirect response with that URL. The browser then navigates to that external domain.

Practice

1. What does res.redirect('/home') do in an Express app?

easy

A. Sends a JSON response with '/home' data

B. Stops the server from running

C. Sends the user to the '/home' URL automatically

D. Logs '/home' to the console

Solution

1. Step 1: Understand res.redirect purpose

   The res.redirect method sends an HTTP redirect response to the client, telling the browser to go to a new URL.

2. Step 2: Analyze the argument '/home'

   Passing '/home' means the user will be redirected to the '/home' path on the same server.

3. Final Answer:

   Sends the user to the '/home' URL automatically -> Option C

4. Quick Check:

   res.redirect('/home') = Redirect to '/home' [OK]

Hint: res.redirect sends user to given URL automatically [OK]

Common Mistakes:

• Thinking it sends JSON data
• Confusing redirect with stopping server
• Assuming it logs to console

2. Which is the correct syntax to redirect permanently to '/dashboard' in Express?

easy

A. res.redirect('/dashboard', 301);

B. res.redirect(301, '/dashboard');

C. res.redirectPermanent('/dashboard');

D. res.redirectPermanent(301, '/dashboard');

Solution

1. Step 1: Recall res.redirect syntax for status code

   Express uses res.redirect(statusCode, url) to specify redirect type.

2. Step 2: Identify correct order of arguments

   The status code (301) must come first, then the URL string.

3. Final Answer:

   res.redirect(301, '/dashboard'); -> Option B

4. Quick Check:

   Status code first, URL second = res.redirect(301, '/dashboard'); [OK]

Hint: Status code goes first in res.redirect(status, url) [OK]

Common Mistakes:

• Swapping arguments order
• Using non-existent res.redirectPermanent method
• Passing status code as second argument

3. What will the browser do after this Express code runs?

app.get('/old', (req, res) => {
  res.redirect('/new');
});

medium

A. Show the content of '/old' page

B. Send a JSON response with '/new' data

C. Return a 404 error

D. Redirect the browser to '/new' URL

Solution

1. Step 1: Understand route handler behavior

   The handler for '/old' calls res.redirect('/new'), which sends a redirect response.

2. Step 2: Browser reaction to redirect

   The browser receives the redirect and automatically requests the '/new' URL instead of '/old'.

3. Final Answer:

   Redirect the browser to '/new' URL -> Option D

4. Quick Check:

   res.redirect('/new') = Browser goes to '/new' [OK]

Hint: res.redirect sends browser to new URL automatically [OK]

Common Mistakes:

• Expecting original page content to show
• Thinking it returns 404 error
• Confusing redirect with JSON response

4. Find the error in this Express code snippet:

app.get('/start', (req, res) => {
  res.redirect('/end', 302);
});

medium

A. The status code should be first argument, not second

B. res.redirect cannot be used inside app.get

C. The URL must be absolute, not relative

D. 302 is not a valid redirect status code

Solution

1. Step 1: Check res.redirect argument order

   Express expects res.redirect(statusCode, url), status code first.

2. Step 2: Identify incorrect argument order

   The code uses res.redirect('/end', 302), which is reversed and causes unexpected behavior.

3. Final Answer:

   The status code should be first argument, not second -> Option A

4. Quick Check:

   Correct order: status, URL [OK]

Hint: Status code must come before URL in res.redirect [OK]

Common Mistakes:

• Swapping status and URL arguments
• Thinking res.redirect can't be used in routes
• Believing relative URLs are invalid
• Assuming 302 is invalid status

5. You want to redirect users from '/login' to '/dashboard' only if they are logged in. Which code correctly uses res.redirect to do this?

hard

A. if (req.user) { res.redirect('/dashboard'); } else { res.send('Please login'); }

B. res.redirect('/dashboard'); if (req.user) { res.send('Welcome'); }

C. res.redirect(302, '/dashboard'); res.send('Logged in');

D. if (!req.user) { res.redirect('/dashboard'); } else { res.send('Please login'); }

Solution

1. Step 1: Check login condition usage

   The code must check if req.user exists to confirm login.

2. Step 2: Redirect only if logged in

   If logged in, redirect to '/dashboard'; otherwise, send a message to login.

3. Step 3: Verify correct use of res.redirect and res.send

   if (req.user) { res.redirect('/dashboard'); } else { res.send('Please login'); } correctly calls res.redirect inside the if block and sends response otherwise, avoiding multiple responses.

4. Final Answer:

   if (req.user) { res.redirect('/dashboard'); } else { res.send('Please login'); } -> Option A

5. Quick Check:

   Redirect only when logged in = if (req.user) { res.redirect('/dashboard'); } else { res.send('Please login'); } [OK]

Hint: Redirect inside if block after login check [OK]

Common Mistakes:

• Calling res.redirect without condition
• Sending multiple responses in one request
• Redirecting when user is not logged in