res.status for status codes in Express - Step-by-Step Execution

Concept Flow - res.status for status codes

Request received

↓

Set status code with res.status(code)

↓

Attach response data (optional)

↓

Send response with res.send() or res.json()

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Client receives response with status code

This flow shows how Express sets HTTP status codes using res.status, then sends the response to the client.

Execution Sample

Express

app.get('/example', (req, res) => {
  res.status(404).send('Not Found');
});

This code sets the HTTP status to 404 and sends a 'Not Found' message to the client.

Execution Table

Step	Action	res.status Code	Response Body	Effect
1	Request to /example received	200	undefined	Server prepares to respond
2	Call res.status(404)	404	undefined	Status code set to 404
3	Call res.send('Not Found')	404	'Not Found'	Response sent with status 404 and body
4	Client receives response	404	'Not Found'	Client sees 404 status and message

💡 Response sent; Express ends request-response cycle

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
res.statusCode	200	404	404	404
res.body	undefined	undefined	'Not Found'	'Not Found'

Key Moments - 2 Insights

Why do we chain res.status(404).send('Not Found') instead of calling them separately?

Because res.status(code) sets the status and returns the res object, allowing chaining. The execution_table row 2 shows status set, and row 3 shows send called on the same res.

What happens if we call res.send() without res.status()?

Express defaults status to 200 OK. The execution_table shows status is 200 before res.status, meaning default 200 is used if not set.

Visual Quiz - 3 Questions

Look at the execution table, what is the status code after step 2?

A undefined

B 404

C 200

D 500

💡 Hint

Check the 'res.status Code' column at step 2 in the execution_table

At which step is the response body set to 'Not Found'?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Response Body' column in the execution_table

If we remove res.status(404), what status code will the client receive?

A 500

B 404

C 200

D 302

💡 Hint

Refer to key_moments answer about default status code when res.status is not called

Concept Snapshot

res.status(code) sets HTTP status code for the response
It returns res to allow chaining like res.status(404).send('msg')
If not set, status defaults to 200 OK
Use res.send() or res.json() to send response body
Always set status before sending response

Full Transcript

In Express, when a request comes in, you can set the HTTP status code using res.status(code). This sets the status code for the response. Then you send the response body using res.send() or res.json(). The status code defaults to 200 if you don't set it. The res.status method returns the res object so you can chain calls like res.status(404).send('Not Found'). This flow ensures the client receives the correct status and message.