Route handlers (GET, POST, PUT, DELETE) in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this GET route handler?

Consider this NestJS controller method handling a GET request. What will be the JSON response when a client calls this route?

NestJS

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

@Controller('items')
export class ItemsController {
  @Get()
  getAll() {
    return { message: 'List of items', count: 3 };
  }
}

A "List of items"

B {"message":"List of items","count":3}

C {"count":3}

D []

💡 Hint

Look at what the method returns and how NestJS sends JSON responses.

The method returns an object with two properties. NestJS automatically converts this object to JSON in the HTTP response.

📝 Syntax

intermediate

Which option correctly defines a POST route handler in NestJS?

You want to create a POST route handler in a NestJS controller. Which code snippet is syntactically correct?

NestJS

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

@Controller('users')
export class UsersController {
  // Your POST handler here
}

A

@Post()
createUser() {
  return 'User created';
}

B

@Post
createUser() {
  return 'User created';
}

C

@Post('/create')
createUser {
  return 'User created';
}

D

@Post('/create')
createUser() {
  return 'User created';
}

💡 Hint

Check the decorator syntax and method declaration carefully.

The @Post decorator requires parentheses even if no path is given. The method must have parentheses after its name.

❓ state_output

advanced

What is the response after calling this PUT route handler?

Given this NestJS PUT route handler, what will be the JSON response when a client sends a PUT request?

NestJS

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

@Controller('products')
export class ProductsController {
  private products = [{ id: 1, name: 'Book' }];

  @Put(':id')
  updateProduct(@Body() body: { name: string }) {
    this.products[0].name = body.name;
    return this.products[0];
  }
}

A {"id":1,"name":null}

B {"id":1,"name":"Book"}

C {"id":1,"name":"Updated"}

D SyntaxError

💡 Hint

The method updates the product name with the value from the request body.

The method changes the first product's name to the value sent in the request body and returns the updated product.

🔧 Debug

advanced

Which option causes an error in this DELETE route handler?

This NestJS controller has a DELETE route handler. Which option will cause a runtime error when the route is called?

NestJS

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

@Controller('tasks')
export class TasksController {
  private tasks = [{ id: 1, title: 'Task 1' }];

  @Delete(':id')
  deleteTask(@Param('id') id: string) {
    const index = this.tasks.findIndex(task => task.id === Number(id));
    if (index === -1) {
      throw new Error('Task not found');
    }
    this.tasks.splice(index, 1);
    return { message: 'Deleted' };
  }
}

A Calling DELETE /tasks/2 throws 'Task not found' error

B Calling DELETE /tasks/abc throws a TypeError

C Calling DELETE /tasks/0 removes the first task

D Calling DELETE /tasks/1 removes the task and returns { message: 'Deleted' }

💡 Hint

Consider what happens when Number(id) is NaN and how findIndex behaves.

When id is 'abc', Number(id) is NaN. The findIndex comparison fails to find a match, returning -1. The code throws 'Task not found' error, not a TypeError.

🧠 Conceptual

expert

Which HTTP method is best suited for updating part of a resource in NestJS?

In NestJS, you want to update only some fields of an existing resource without replacing it entirely. Which HTTP method and decorator should you use?

A Use @Patch() to update part of the resource

B Use @Put() to update the entire resource

C Use @Post() to update part of the resource

D Use @Delete() to update part of the resource

💡 Hint

Think about the difference between PUT and PATCH in HTTP methods.

PUT replaces the entire resource, while PATCH updates only specified fields. NestJS supports both with @Put() and @Patch() decorators.

Practice

1. Which decorator is used in NestJS to create a route handler that responds to HTTP GET requests?

easy

A. @Get

B. @Post

C. @Put

D. @Delete

Solution

1. Step 1: Understand HTTP methods and their decorators

   In NestJS, each HTTP method has a specific decorator: @Get for GET, @Post for POST, @Put for PUT, and @Delete for DELETE.

2. Step 2: Match the decorator to the GET method

   The decorator @Get is specifically designed to handle HTTP GET requests.

3. Final Answer:

   @Get -> Option A

4. Quick Check:

   GET method uses @Get decorator [OK]

Hint: GET requests use @Get decorator in NestJS [OK]

Common Mistakes:

• Confusing @Post or @Put with @Get
• Using @Delete for GET requests
• Not using any decorator

2. Which of the following is the correct syntax to define a POST route handler in a NestJS controller?

easy

A. @Post('/create') createItem() {}

B. Post('/create') createItem() {}

C. @post('/create') createItem() {}

D. @Put('/create') createItem() {}

Solution

1. Step 1: Check the decorator syntax

   Decorators in NestJS start with '@' and are case-sensitive. The correct decorator for POST is '@Post'.

2. Step 2: Verify the route path and method name

   The route path '/create' is correctly passed as a string argument, and the method name is valid.

3. Final Answer:

   @Post('/create') createItem() {} -> Option A

4. Quick Check:

   Correct decorator syntax uses '@Post' with parentheses [OK]

Hint: Decorators start with '@' and are case-sensitive [OK]

Common Mistakes:

• Missing '@' before decorator
• Using lowercase '@post' instead of '@Post'
• Using wrong decorator like '@Put' for POST

3. Given the following NestJS controller code, what will be the HTTP method and route path to access the handler?

@Controller('users')
export class UserController {
  @Put(':id')
  updateUser() {
    return 'User updated';
  }
}

medium

A. GET /users/:id

B. DELETE /users/:id

C. PUT /users/:id

D. POST /users/:id

Solution

1. Step 1: Identify the controller base path

   The @Controller('users') decorator sets the base route path to '/users'.

2. Step 2: Identify the route handler method and path

   The @Put(':id') decorator means this handler responds to HTTP PUT requests at the path '/users/:id', where ':id' is a route parameter.

3. Final Answer:

   PUT /users/:id -> Option C

4. Quick Check:

   @Put with ':id' means PUT method at /users/:id [OK]

Hint: Decorator @Put means HTTP PUT method [OK]

Common Mistakes:

• Confusing @Put with @Get or @Post
• Ignoring the controller base path
• Misreading ':id' as a literal string

4. What is wrong with this NestJS route handler code?

@Controller('items')
export class ItemController {
  @Delete('/remove')
  removeItem() {
    console.log('Item removed');
  }
}

medium

A. The method name must be 'deleteItem' for @Delete decorator

B. The decorator @Delete cannot have a path argument

C. The controller path 'items' is invalid

D. The method should return a value, not just console.log

Solution

1. Step 1: Check the decorator and path usage

   @Delete can have a path argument like '/remove', so this is valid.

2. Step 2: Check the method implementation

   The method only logs to console but does not return any response. HTTP handlers should return a response to the client.

3. Final Answer:

   The method should return a value, not just console.log -> Option D

4. Quick Check:

   Route handlers must return a response [OK]

Hint: Route handlers must return a response, not just log [OK]

Common Mistakes:

• Assuming console.log sends response
• Thinking decorator cannot have path
• Believing method name must match decorator

5. You want to create a NestJS controller with a route handler that updates a product by its ID using HTTP PUT. The handler should accept the ID as a route parameter and the updated data in the request body. Which code snippet correctly implements this?

hard

A. @Put updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; }

B. @Put(':id') updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; }

C. @Put(':id') updateProduct(id: string, data: any) { return `Updated product ${id}`; }

D. @Post(':id') updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; }

Solution

1. Step 1: Use the correct HTTP method and route parameter

   Updating a resource uses HTTP PUT, so @Put(':id') is correct to capture the ID as a route parameter.

2. Step 2: Use parameter decorators to access route and body data

   @Param('id') extracts the ID from the route, and @Body() extracts the request body data. Both are required for this handler.

3. Step 3: Check method signature and return

   The method correctly returns a string confirming the update with the ID.

4. Final Answer:

   @Put(':id') updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; } -> Option B

5. Quick Check:

   Use @Put with ':id' and @Param plus @Body [OK]

Hint: Use @Put(':id') with @Param and @Body for updates [OK]

Common Mistakes:

• Missing route parameter in @Put decorator
• Not using @Param or @Body decorators
• Using wrong HTTP method like @Post for update