res.redirect for redirections in Express - Step-by-Step Execution

Concept Flow - res.redirect for redirections

Client sends request

↓

Server receives request

↓

Server calls res.redirect(url)

↓

Server sends 302 status + Location header

↓

Client receives redirect response

↓

Client automatically requests new URL

↓

New resource served to client

This flow shows how a server tells the browser to go to a new URL using res.redirect, causing the browser to request that new URL.

Execution Sample

Express

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

When a client requests '/old-page', the server responds by redirecting them to '/new-page'.

Execution Table

Step	Action	Server Response	Client Behavior
1	Client requests '/old-page'	No response yet	Sends HTTP GET to server
2	Server receives request	No response yet	Waiting for server response
3	Server calls res.redirect('/new-page')	Sends HTTP 302 status with Location: /new-page header	Receives redirect response
4	Client receives 302 redirect	Response sent	Automatically requests '/new-page' URL
5	Server receives new request for '/new-page'	Processes and sends resource	Receives new page content
6	Client renders '/new-page' content	Response complete	Displays new page to user

💡 Redirect completed when client requests and receives the new URL content.

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
requestedURL	undefined	/old-page	/new-page	/new-page
responseStatus	undefined	302	200	200
responseHeaders.Location	undefined	/new-page	undefined	undefined

Key Moments - 2 Insights

Why does the client make a second request after res.redirect is called?

Because res.redirect sends a 302 status with a Location header telling the client to go to a new URL, so the client automatically requests that new URL (see execution_table step 4).

Does res.redirect send the content of the new page immediately?

No, it only sends a redirect response (302 status and Location header). The client must request the new page separately (see execution_table steps 3 and 5).

Visual Quiz - 3 Questions

Look at the execution table, what HTTP status code does the server send when res.redirect is called?

A 404

B 302

C 200

D 500

💡 Hint

Check the 'Server Response' column at step 3 in the execution_table.

At which step does the client send the request for the new URL after redirection?

A Step 4

B Step 5

C Step 2

D Step 6

💡 Hint

Look at the 'Client Behavior' column to see when the new URL request happens.

If the server changed res.redirect('/new-page') to res.redirect(301, '/new-page'), what would change in the execution table?

A The client would not request the new URL

B The server would send the new page content immediately

C The status code at step 3 would be 301 instead of 302

D No change at all

💡 Hint

Focus on the 'Server Response' status code at step 3.

Concept Snapshot

res.redirect(url) sends a 302 redirect response to the client.
The client then requests the new URL automatically.
The server does NOT send the new page content immediately.
Use res.redirect(status, url) to specify other redirect codes like 301.
Commonly used to move users from old URLs to new ones.

Full Transcript

When a client asks the server for a page, the server can tell the client to go somewhere else by using res.redirect. This sends a special response with status 302 and a Location header. The client sees this and automatically asks for the new page. The server then sends the new page content. This process helps move users smoothly from one URL to another without confusion.

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