Method chaining on response in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Express response chaining?

Consider this Express route handler code. What will the client receive as the response body?

Express

app.get('/test', (req, res) => {
  res.status(201).type('text/plain').send('Success');
});

A The client receives a plain text response with status 201 and body 'Success'.

B The client receives a JSON response with status 200 and body 'Success'.

C The client receives a plain text response with status 200 and body 'Success'.

D The client receives a JSON response with status 201 and body 'Success'.

💡 Hint

Remember that method chaining sets status, content type, and then sends the body.

The status(201) sets the HTTP status code to 201. The type('text/plain') sets the Content-Type header to plain text. Finally, send('Success') sends the string as the response body. So the client gets status 201, plain text content type, and body 'Success'.

📝 Syntax

intermediate

Which option correctly chains methods to send JSON with status 404?

Choose the correct Express response chaining to send a JSON error message with status 404.

A res.status(404).sendJson({ error: 'Not found' });

B res.json({ error: 'Not found' }).status(404);

C res.send({ error: 'Not found' }).status(404);

D res.status(404).json({ error: 'Not found' });

💡 Hint

The status must be set before sending the response.

Method chaining requires setting the status before sending the response. res.status(404).json(...) correctly sets status 404 and sends JSON. Option D tries to set status after sending, which won't work. Option D uses send which sends JSON but chaining status after send is invalid. Option D uses a non-existent method sendJson.

🔧 Debug

advanced

Why does this chained response code cause an error?

Examine the code below. Why will it cause an error or unexpected behavior?

Express

app.get('/error', (req, res) => {
  res.send('First response').status(200);
});

A Because status(200) is invalid and should be statusCode(200).

B Because send cannot be called without a JSON object.

C Because status must be set before send; chaining status after send does nothing or errors.

D Because res.send returns undefined and chaining is not allowed.

💡 Hint

Think about the order of method calls and when headers are sent.

Calling res.send() sends the response immediately, including headers. Trying to set status after sending has no effect or may cause an error because headers are already sent. The correct order is to set status first, then send.

❓ state_output

advanced

What is the final status code sent to the client?

Given this Express code, what status code will the client receive?

Express

app.get('/chain', (req, res) => {
  res.status(202).status(204).send('Done');
});

A 202

B 204

C 200

D Error thrown due to multiple status calls

💡 Hint

Later status calls overwrite earlier ones.

Calling res.status(202) sets status to 202, but then res.status(204) overwrites it to 204. The last status call before send determines the final status code.

🧠 Conceptual

expert

Which statement about Express response method chaining is TRUE?

Select the true statement about method chaining on Express response objects.

A Calling res.send() ends the response and further chaining methods have no effect.

B You can chain res.send() multiple times to send multiple responses.

C res.json() cannot be chained with res.status() because they return different objects.

D res.status() must always be called after res.send() to set the status code correctly.

💡 Hint

Think about when the response is finalized.

Once res.send() is called, the response is sent and closed. Any further method calls on res do not affect the response. You cannot send multiple responses for one request. res.status() must be called before res.send(). Both res.status() and res.json() return the response object, so chaining is possible.