res.send for general responses in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does res.send() do in Express?

res.send() sends a response back to the client. It can send strings, objects, or buffers as the HTTP response body.

beginner

Can res.send() send JSON objects directly?

Yes, if you pass an object to res.send(), Express converts it to JSON and sets the Content-Type header to application/json.

intermediate

What happens if you call res.send() multiple times in one request?

Only the first call to res.send() sends the response. Subsequent calls are ignored or cause errors because the response is already sent.

intermediate

How does res.send() differ from res.json()?

res.send() can send any type of response (string, buffer, object), while res.json() specifically sends JSON and sets the Content-Type header to application/json.

beginner

What is a simple example of using res.send() to send a text response?

app.get('/hello', (req, res) => {
  res.send('Hello, friend!');
});

This sends the text 'Hello, friend!' to the browser.

What type of data can res.send() send in Express?

A Only HTML files

B Only strings

C Only JSON objects

D Strings, objects, buffers

res.send() can send strings, objects (which it converts to JSON), and buffers as responses.

If you pass an object to res.send(), what does Express do?

A Converts it to JSON and sets Content-Type to application/json

B Throws an error

C Sends it as plain text

D Ignores the object and sends nothing

Express automatically converts objects to JSON and sets the correct header.

What happens if you call res.send() twice in the same route handler?

A Both responses are sent one after another

B The second call overwrites the first response

C Only the first call sends a response; the second is ignored or causes an error

D Express queues both responses and sends them together

Once the response is sent, you cannot send another one for the same request.

Which method is more specific for sending JSON responses?

A res.render()

B res.json()

C res.send()

D res.redirect()

res.json() is designed specifically to send JSON responses.

What header does Express set automatically when sending an object with res.send()?

A Content-Type: application/json

B Content-Type: text/html

C Content-Type: text/plain

D Content-Type: application/xml

Express sets the Content-Type header to application/json when sending objects.

Explain how res.send() works in Express and what types of data it can send.

Think about what happens when you pass different data types to res.send()

Describe the difference between res.send() and res.json() in Express.

Consider when you want to send JSON specifically versus other data

Practice

1. What does res.send() do in an Express app?

easy

A. Logs information to the console

B. Sends a response back to the client and ends the request

C. Reads data from the client request

D. Starts a new server

Solution

1. Step 1: Understand the purpose of res.send()

   res.send() is used to send a response back to the client in Express.

2. Step 2: Recognize that it ends the response

   After sending data, res.send() automatically ends the response, so no more data is sent.

3. Final Answer:

   Sends a response back to the client and ends the request -> Option B

4. Quick Check:

   res.send() = sends response [OK]

Hint: Remember: res.send sends and finishes response [OK]

Common Mistakes:

• Thinking res.send starts the server
• Confusing res.send with reading request data
• Assuming res.send logs to console

2. Which of the following is the correct syntax to send a plain text response using res.send?

easy

A. res.send('Hello');

B. res.send[Hello];

C. res.send({ message: 'Hello' });

D. res.send = 'Hello';

Solution

1. Step 1: Identify correct method call syntax

   The correct way to call res.send is as a function with parentheses and the data inside.

2. Step 2: Check the options for valid syntax

   res.send('Hello'); uses res.send('Hello'); which is correct. res.send({ message: 'Hello' }); sends an object, which is valid but not plain text. Options B and D have invalid syntax.

3. Final Answer:

   res.send('Hello'); -> Option A

4. Quick Check:

   Correct function call = res.send('text') [OK]

Hint: Use parentheses and quotes: res.send('text') [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Assigning value instead of calling function
• Sending object when plain text is needed

3. What will the client receive when this Express route runs?

app.get('/test', (req, res) => {
  res.send({ success: true });
});

medium

A. A plain text: '[object Object]'

B. Nothing, response is empty

C. An error because object can't be sent

D. A JSON string: '{"success":true}'

Solution

1. Step 1: Understand res.send with an object

   When res.send() receives an object, Express converts it to JSON automatically.

2. Step 2: Predict the client response

   The client will get a JSON string representing the object: '{"success":true}'.

3. Final Answer:

   A JSON string: '{"success":true}' -> Option D

4. Quick Check:

   res.send(object) = JSON string [OK]

Hint: Objects sent with res.send become JSON strings [OK]

Common Mistakes:

• Expecting plain text '[object Object]'
• Thinking it causes an error
• Assuming empty response

4. Identify the error in this Express route:

app.get('/hello', (req, res) => {
  res.send('Hello');
  res.send('Again');
});

medium

A. Calling res.send twice causes an error

B. Missing semicolon after res.send

C. res.send cannot send strings

D. Route path is invalid

Solution

1. Step 1: Check multiple res.send calls in one route

   Once res.send() is called, the response is finished and cannot be sent again.

2. Step 2: Understand the error caused

   Calling res.send() a second time causes an error because the response is already closed.

3. Final Answer:

   Calling res.send twice causes an error -> Option A

4. Quick Check:

   Only one res.send per response [OK]

Hint: Send response once; multiple res.send calls cause errors [OK]

Common Mistakes:

• Ignoring that response ends after first send
• Thinking multiple sends append data
• Blaming syntax or route path

5. You want to send a JSON response with a status code 201 and a message 'Created' using res.send. Which code correctly does this?

hard

A. res.send({ status: 201, message: 'Created' });

B. res.send(201, { message: 'Created' });

C. res.status(201).send({ message: 'Created' });

D. res.status(201).send('Created');

Solution

1. Step 1: Set status code before sending response

   Use res.status(201) to set the HTTP status code to 201.

2. Step 2: Send JSON object with message

   Chain .send({ message: 'Created' }) to send the JSON response.

3. Final Answer:

   res.status(201).send({ message: 'Created' }); -> Option C

4. Quick Check:

   Status then send JSON = res.status(201).send({ message: 'Created' }); [OK]

Hint: Chain res.status(code).send(data) to set status and send [OK]

Common Mistakes:

• Passing status code as first argument to send
• Sending status inside JSON instead of HTTP status
• Sending plain text when JSON is needed