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.