Method chaining on response in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send a JSON response with status 200.

Express

res.status(200).[1]({ message: 'Success' });

Drag options to blanks, or click blank then click option'

Ajson

Bend

Csend

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using send instead of json causes the response to be sent as plain text.

Using end does not send JSON data.

The json method sends a JSON response and allows chaining after setting status.

2fill in blank

medium

Complete the code to set a header and send a plain text response.

Express

res.set('Content-Type', 'text/plain').[1]('Hello World');

Drag options to blanks, or click blank then click option'

Ajson

Bend

Cwrite

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using json sends JSON format, not plain text.

Using end does not allow chaining after setting headers.

The send method sends the response body and supports chaining after setting headers.

3fill in blank

hard

Fix the error in chaining to set status and send a response.

Express

res.[1](404).send('Not Found');

Drag options to blanks, or click blank then click option'

Astatus

BsendStatus

CsetStatus

DwriteStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using sendStatus ends the response and chaining send after causes error.

Using setStatus or writeStatus are not valid Express methods.

The correct method to set status for chaining is status. sendStatus sends the response immediately and does not allow chaining.

4fill in blank

hard

Fill both blanks to set a cookie and send a JSON response.

Express

res.[1]('token', 'abc123').[2]({ success: true });

Drag options to blanks, or click blank then click option'

Acookie

Bjson

Csend

DsetHeader

Attempts:

3 left

💡 Hint

Common Mistakes

Using setHeader instead of cookie does not set cookies properly.

Using send instead of json sends plain text, not JSON.

The cookie method sets a cookie and allows chaining. The json method sends a JSON response.

5fill in blank

hard

Fill all three blanks to set status, header, and send a plain text response.

Express

res.[1](201).[2]('X-Custom', '123').[3]('Created');

Drag options to blanks, or click blank then click option'

Astatus

Bset

Csend

Djson

Attempts:

3 left

💡 Hint

Common Mistakes

Using json instead of send sends JSON, not plain text.

Using setHeader instead of set is not the Express method.

Use status to set HTTP status, set to set headers, and send to send the response body as plain text.

Practice

1. What does method chaining on the Express res object allow you to do?

easy

A. Combine multiple response methods in one line for cleaner code

B. Run multiple server instances simultaneously

C. Chain database queries with response methods

D. Automatically restart the server on errors

Solution

1. Step 1: Understand method chaining concept

   Method chaining means calling multiple methods one after another on the same object.

2. Step 2: Apply to Express response object

   Express res allows chaining methods like status(), set(), and send() to write concise code.

3. Final Answer:

   Combine multiple response methods in one line for cleaner code -> Option A

4. Quick Check:

   Method chaining = Combine methods [OK]

Hint: Think of chaining like linking commands in one line [OK]

Common Mistakes:

• Confusing method chaining with running multiple servers
• Mixing database queries with response methods
• Assuming chaining restarts the server

2. Which of the following is the correct way to chain methods on the Express res object?

easy

A. res.set('Content-Type', 'text/plain').status(200).send('OK')

B. res.status(200).send('OK').set('Content-Type', 'text/plain')

C. res.send('OK').status(200).set('Content-Type', 'text/plain')

D. res.status(200); res.send('OK'); res.set('Content-Type', 'text/plain')

Solution

1. Step 1: Check method chaining order

   Methods like status() and set() return the res object, allowing chaining before send().

2. Step 2: Identify correct chain ending

   The chain must end with send() to send the response and finish the chain.

3. Final Answer:

   res.set('Content-Type', 'text/plain').status(200).send('OK') -> Option A

4. Quick Check:

   Chain ends with send() [OK]

Hint: Always end chain with send() or end() [OK]

Common Mistakes:

• Calling send() before setting status or headers
• Trying to chain after send()
• Using semicolons instead of chaining dots

3. What will be the output of this Express code snippet?

app.get('/', (req, res) => {
  res.status(404).set('Content-Type', 'text/plain').send('Not Found');
});

medium

A. Response with status 200 and body 'Not Found'

B. Syntax error due to incorrect chaining

C. Response with status 404 and empty body

D. Response with status 404 and body 'Not Found' with plain text content type

Solution

1. Step 1: Analyze method chain

   The code sets status to 404, sets content type header, then sends 'Not Found' as body.

2. Step 2: Understand response behavior

   The response will have status 404, header 'Content-Type: text/plain', and body 'Not Found'.

3. Final Answer:

   Response with status 404 and body 'Not Found' with plain text content type -> Option D

4. Quick Check:

   Status 404 + send body 'Not Found' [OK]

Hint: Status and headers set before send() affect response [OK]

Common Mistakes:

• Assuming default status 200 is sent
• Thinking body is empty
• Believing chaining causes syntax error

4. Identify the error in this Express response chaining code:

res.send('Hello').status(200).set('Content-Type', 'text/html');

medium

A. No error, code works fine

B. Cannot chain methods after send() because response is already sent

C. Missing semicolon after send()

D. set() method does not exist on res object

Solution

1. Step 1: Understand send() behavior

   Calling send() sends the response and ends it, so chaining after it is invalid.

2. Step 2: Identify chaining error

   Methods status() and set() cannot be called after send() because response is finished.

3. Final Answer:

   Cannot chain methods after send() because response is already sent -> Option B

4. Quick Check:

   send() ends response, no chaining after [OK]

Hint: send() ends response; no chaining after it [OK]

Common Mistakes:

• Thinking chaining after send() is allowed
• Confusing semicolon placement with chaining error
• Believing set() is not a valid method

5. You want to send a JSON response with status 201 and a custom header X-Custom set to Success. Which of the following chained methods is correct?

hard

A. res.status(201).send({ message: 'Created' }).set('X-Custom', 'Success');

B. res.status(201).json({ message: 'Created' }); res.set('X-Custom', 'Success');

C. res.set('X-Custom', 'Success').status(201).json({ message: 'Created' });

D. res.json({ message: 'Created' }).status(201).set('X-Custom', 'Success');

Solution

1. Step 1: Order methods correctly

   Set headers first, then status, then send JSON with json() method.

2. Step 2: Avoid chaining after response sent

   Methods after json() or send() won't work because response ends.

3. Final Answer:

   res.set('X-Custom', 'Success').status(201).json({ message: 'Created' }); -> Option C

4. Quick Check:

   Headers + status + json() in chain [OK]

Hint: Set headers and status before json() or send() [OK]

Common Mistakes:

• Chaining set() after send() or json()
• Sending response before setting headers
• Using multiple separate statements instead of chaining