res.status for status codes in Express - Mini Project: Build & Apply

Using res.status to Send HTTP Status Codes in Express

📖 Scenario: You are building a simple Express server that responds to client requests. You want to send proper HTTP status codes to tell the client if the request was successful or if there was an error.

🎯 Goal: Build an Express route that uses res.status to send different HTTP status codes along with messages.

📋 What You'll Learn

Create an Express app with a GET route at /status

Add a variable isSuccess to control the response status

Use res.status to send 200 if isSuccess is true

Use res.status to send 500 if isSuccess is false

Send a JSON message with a message property describing the status

💡 Why This Matters

🌍 Real World

Web servers use HTTP status codes to tell browsers or apps if requests worked or failed. This helps users understand what happened.

💼 Career

Backend developers must send correct status codes to build reliable APIs and web services.

1

Set up Express app and route

Create an Express app by requiring express and calling express(). Then create a GET route at /status with a callback function that takes req and res as parameters.

Express

const express = require('express');
const app = express();

// Create GET route at /status
// Your code here

Hint

Remember to require Express and create an app instance. Use app.get to define the route.

2

Add a variable to control success

Inside the /status route callback, create a variable called isSuccess and set it to true.

Express

const express = require('express');
const app = express();

app.get('/status', (req, res) => {
  // Create variable isSuccess and set to true
  // Your code here
});

Hint

Just create a constant named isSuccess and assign it the value true.

3

Send status 200 or 500 based on isSuccess

Use an if statement to check if isSuccess is true. If yes, use res.status(200) and send a JSON object with { message: 'Success' }. Otherwise, use res.status(500) and send { message: 'Error' }.

Express

const express = require('express');
const app = express();

app.get('/status', (req, res) => {
  const isSuccess = true;
  // Use if to check isSuccess and send status and JSON message
  // Your code here
});

Hint

Use res.status(code).json(object) to send status and JSON response.

4

Start the server on port 3000

Add code to start the Express server by calling app.listen on port 3000 with a callback that logs 'Server running on port 3000'.

Express

const express = require('express');
const app = express();

app.get('/status', (req, res) => {
  const isSuccess = true;
  if (isSuccess) {
    res.status(200).json({ message: 'Success' });
  } else {
    res.status(500).json({ message: 'Error' });
  }
});

// Start server on port 3000
// Your code here

Hint

Use app.listen(port, callback) to start the server and log a message.

Practice

1. What does res.status(404) do in an Express route handler?

easy

A. Changes the request method to GET

B. Sends a 404 error message to the client automatically

C. Sets the HTTP response status code to 404 (Not Found)

D. Stops the server from running

Solution

1. Step 1: Understand the purpose of res.status

   res.status(code) sets the HTTP status code for the response but does not send the response itself.

2. Step 2: Identify what 404 means

   404 is the standard HTTP status code meaning "Not Found".

3. Final Answer:

   Sets the HTTP response status code to 404 (Not Found) -> Option C

4. Quick Check:

   res.status(404) = sets status code 404 [OK]

Hint: res.status sets code; use res.send or res.json to send [OK]

Common Mistakes:

• Thinking res.status sends the response automatically
• Confusing status code with request method
• Assuming res.status stops server execution

2. Which of the following is the correct way to send a 201 status with a JSON response in Express?

easy

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

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

C. res.json(201, { message: 'Created' })

D. res.status(201).json({ message: 'Created' })

Solution

1. Step 1: Recall correct chaining syntax

   In Express, res.status(code) sets the status code, then res.json(data) sends the JSON response.

2. Step 2: Check each option's syntax

   res.status(201).json({ message: 'Created' }) correctly chains res.status(201) with res.json({ message: 'Created' }). Others misuse method order or parameters.

3. Final Answer:

   res.status(201).json({ message: 'Created' }) -> Option D

4. Quick Check:

   Correct chaining = res.status().json() [OK]

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

Common Mistakes:

• Calling res.send before res.status
• Passing status code as first argument to res.json
• Using res.status.json which is invalid

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

app.get('/test', (req, res) => {
  res.status(500);
  res.send('Server error');
});

medium

A. A response with status 200 and body 'Server error'

B. A response with status 500 and body 'Server error'

C. A response with status 500 and empty body

D. An error thrown by Express

Solution

1. Step 1: Analyze res.status and res.send usage

   res.status(500) sets the HTTP status code to 500. Then res.send('Server error') sends the response body with that status.

2. Step 2: Determine final response

   The client receives status 500 with the text 'Server error' as the body.

3. Final Answer:

   A response with status 500 and body 'Server error' -> Option B

4. Quick Check:

   res.status(500) + res.send('Server error') = 500 + body [OK]

Hint: res.status sets code; res.send sends body with that code [OK]

Common Mistakes:

• Assuming res.send resets status to 200
• Thinking status 500 causes Express error automatically
• Believing response body is empty without res.send argument

4. Identify the error in this Express code snippet:

app.get('/error', (req, res) => {
  res.send('Oops!');
  res.status(400);
});

medium

A. res.status(400) is called after res.send, so status code is ignored

B. res.send cannot be called without res.status first

C. res.status must be called with a string, not a number

D. No error, this code works correctly

Solution

1. Step 1: Understand response flow in Express

   Once res.send() is called, the response is sent and closed. Any code after it won't affect the response.

2. Step 2: Analyze order of calls

   Here, res.send('Oops!') sends the response with default status 200. Then res.status(400) is called but ignored because response is already sent.

3. Final Answer:

   res.status(400) is called after res.send, so status code is ignored -> Option A

4. Quick Check:

   Call res.status before res.send to set status [OK]

Hint: Always call res.status before res.send or res.json [OK]

Common Mistakes:

• Calling res.status after res.send expecting status change
• Thinking res.send requires res.status first
• Using string instead of number in res.status

5. You want to send a 204 No Content status with no response body in Express. Which code snippet correctly does this?

hard

A. res.status(204).send()

B. All of the above

C. res.status(204).json(null)

D. res.sendStatus(204)

Solution

1. Step 1: Understand 204 No Content meaning

   Status 204 means the server successfully processed the request but returns no content in the response body (Content-Length: 0).

2. Step 2: Check each option's behavior

   res.status(204).send() sends status 204 with empty body [check].
   res.status(204).json(null) sends status 204 with JSON "null" body ✗.
   res.sendStatus(204) sends status 204 with "No Content" text body ✗.
   Only A sends no response body.

3. Final Answer:

   res.status(204).send() -> Option A

4. Quick Check:

   res.status(204).send() = 204 + empty body [OK]

Hint: Use res.status(204).send() for 204 with no body [OK]

Common Mistakes:

• Sending body content with 204 status (should be empty)
• Using res.status(204).json({}) which sends empty object body
• Not sending response after setting status