Status codes and headers in NestJS - Mini Project: Build & Apply

Status codes and headers

📖 Scenario: You are building a simple NestJS API that responds to client requests with proper HTTP status codes and custom headers. This helps clients understand the result of their requests and receive extra information.

🎯 Goal: Create a NestJS controller with one GET endpoint that returns a JSON message. Set a custom HTTP status code and add a custom header to the response.

📋 What You'll Learn

Create a controller named AppController

Add a GET route handler method named getHello

Set the HTTP status code to 201 (Created) for the response

Add a custom header X-Custom-Header with value NestJS

Return a JSON object with a message property set to 'Hello World'

💡 Why This Matters

🌍 Real World

APIs often need to send specific status codes and headers to inform clients about the result of their requests and provide extra metadata.

💼 Career

Understanding how to control HTTP status codes and headers is essential for backend developers building RESTful APIs with NestJS.

1

Create the controller and GET method

Create a NestJS controller class named AppController. Inside it, add a method named getHello decorated with @Get() that returns an object { message: 'Hello World' }.

NestJS

import { Controller, Get } from '@nestjs/common';

@Controller()
export class AppController {
  // Your code here
}

Hint

Use @Controller() to define the controller and @Get() to define the GET route handler.

2

Add HTTP status code 201

Import @HttpCode from @nestjs/common. Add the decorator @HttpCode(201) above the getHello method to set the HTTP status code to 201.

NestJS

import { Controller, Get, HttpCode } from '@nestjs/common';

@Controller()
export class AppController {
  @Get()
  // Your code here
  getHello() {
    return { message: 'Hello World' };
  }
}

Hint

The @HttpCode() decorator sets the response status code.

3

Inject response object to set headers

Import Res and Response from @nestjs/common and express respectively. Modify the getHello method to accept a parameter res decorated with @Res() and typed as Response. Use res.setHeader('X-Custom-Header', 'NestJS') to add the custom header. Then send the JSON response using res.status(201).json({ message: 'Hello World' }).

NestJS

import { Controller, Get, HttpCode, Res } from '@nestjs/common';
import { Response } from 'express';

@Controller()
export class AppController {
  @Get()
  @HttpCode(201)
  getHello(@Res() res: Response) {
    // Your code here
  }
}

Hint

Use the @Res() decorator to get the response object and set headers before sending the response.

4

Complete the controller with proper imports

Ensure the imports include Controller, Get, HttpCode, and Res from @nestjs/common, and Response from express. The AppController class should have the getHello method as defined with the custom header and status code.

NestJS

import { Controller, Get, HttpCode, Res } from '@nestjs/common';
import { Response } from 'express';

// Verify all code is present and correct
// Your code here

Hint

Check that all imports and method code are correct and complete.

Practice

1. In NestJS, what does the HTTP status code 201 usually indicate in a response?

easy

A. A new resource was successfully created

B. The request was malformed or invalid

C. The requested resource was not found

D. The server encountered an internal error

Solution

1. Step 1: Understand HTTP status codes

   HTTP status codes communicate the result of a client's request. Code 201 means "Created".

2. Step 2: Match 201 with its meaning

   201 specifically means a new resource was successfully created on the server.

3. Final Answer:

   A new resource was successfully created -> Option A

4. Quick Check:

   201 = Created [OK]

Hint: 201 means resource created successfully [OK]

Common Mistakes:

• Confusing 201 with 404 (not found)
• Thinking 201 means server error
• Mixing 201 with 400 (bad request)

2. Which of the following is the correct way to set a custom header X-Custom-Header with value 123 in a NestJS controller using Express response?

easy

A. res.setHeader('X-Custom-Header', 789);

B. res.set('X-Custom-Header', '123');

C. res.header('X-Custom-Header', '789');

D. res.addHeader('X-Custom-Header', '123');

Solution

1. Step 1: Recall Express response methods

   Express response object uses res.set() to set headers.

2. Step 2: Check method and value types

   res.set() accepts header name and string value. res.set('X-Custom-Header', '123'); uses correct method and string value.

3. Final Answer:

   res.set('X-Custom-Header', '123'); -> Option B

4. Quick Check:

   Use res.set() to set headers [OK]

Hint: Use res.set() to set headers in NestJS [OK]

Common Mistakes:

• Using res.setHeader (not Express method)
• Passing number instead of string as header value
• Using non-existent res.addHeader method

3. What will be the HTTP status code and header in the response when this NestJS controller method runs?

async getData(@Res() res) {
  res.status(204).set('X-Info', 'No Content').send();
}

medium

A. Status 204 with no headers

B. Status 200 with header X-Info: No Content

C. Status 204 with header X-Info: No Content

D. Status 404 with header X-Info: No Content

Solution

1. Step 1: Analyze status and header setting

   The code sets status to 204 and header 'X-Info' to 'No Content'.

2. Step 2: Understand 204 status behavior

   Status 204 means "No Content" and allows custom headers. The header is set correctly.

3. Final Answer:

   Status 204 with header X-Info: No Content -> Option C

4. Quick Check:

   Status 204 + header set = Status 204 with header X-Info: No Content [OK]

Hint: res.status(204).set() sets status and headers [OK]

Common Mistakes:

• Assuming 204 means no headers allowed
• Confusing default status 200 with explicit 204
• Ignoring header set after status

4. Identify the error in this NestJS controller method that tries to set status and headers:

async update(@Res() res) {
  res.status(200);
  res.set('Content-Type', 'application/json');
  res.send({ success: true });
  res.status(201);
}

medium

A. Calling res.status(201) after res.send() has no effect

B. res.set() must be called before res.status()

C. res.send() cannot send JSON objects

D. res.status() cannot be called twice

Solution

1. Step 1: Review response flow

   res.send() sends the response and ends it. Any code after it won't affect response.

2. Step 2: Check status calls order

   Calling res.status(201) after res.send() does nothing because response is already sent.

3. Final Answer:

   Calling res.status(201) after res.send() has no effect -> Option A

4. Quick Check:

   res.send() ends response, later status calls ignored [OK]

Hint: Set status before res.send(), not after [OK]

Common Mistakes:

• Trying to set status after sending response
• Thinking res.send() can't send JSON
• Believing res.set() must come before res.status()

5. You want to send a 202 Accepted status with a custom header X-Request-ID and a JSON body in NestJS. Which code snippet correctly achieves this?

hard

A. res.send({ message: 'Accepted' }).status(202).set('X-Request-ID', requestId);

B. res.set('X-Request-ID', requestId).status(202).send('Accepted');

C. res.status(202).send({ message: 'Accepted' }).set('X-Request-ID', requestId);

D. res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' });

Solution

1. Step 1: Order of method calls matters

   In Express, chaining status, set, and json works if status is set before sending.

2. Step 2: Check each option's correctness

   Options A and C call send before completing status/header setup, invalid. res.set('X-Request-ID', requestId).status(202).send('Accepted'); sets header and status but uses res.send('Accepted') sending plain text instead of JSON object. res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' }); correctly sets status, header, sends JSON.

3. Step 3: Confirm best practice

   res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' }); is the clearest and most common pattern: status, set header, then send JSON.

4. Final Answer:

   res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' }); -> Option D

5. Quick Check:

   Status then headers then send JSON [OK]

Hint: Chain status, set, then send/json in that order [OK]

Common Mistakes:

• Calling send before setting status or headers
• Using send instead of json for JSON body
• Setting headers after sending response