Controller decorator in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the route path for this controller?

Given the following NestJS controller code, what is the base route path that this controller will handle?

NestJS

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

@Controller('users')
export class UsersController {
  @Get()
  findAll() {
    return 'List of users';
  }
}

A /users/findAll

B /

C /users

D /getUsers

💡 Hint

The string inside @Controller defines the base route path for all methods inside the controller.

The @Controller('users') decorator sets the base route path to /users. The @Get() decorator on findAll() means it handles GET requests at the base path, so the full route is /users.

📝 Syntax

intermediate

Which option causes a syntax error in this controller?

Identify which controller code snippet will cause a syntax error in NestJS.

A

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

@Controller('orders')
export class OrdersController {
  @Get()
  getOrders() {
    return 'Orders list';
  }
}

B

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

@Controller('customers')
export class CustomersController {
  @Get()
  fetch() {
    return 'Customer data';
  }
}

C

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

@Controller('categories')
export class CategoriesController {
  @Get()
  list() {
    return 'Category list';
  }
}

D

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

@Controller('products')
export class ProductsController {
  @Get()
  getAll() {
    return 'All products';
  }
}

💡 Hint

Check if the decorator syntax is correct with parentheses.

Option A misses parentheses after @Get. Decorators must be called as functions, so @Get() is required. This causes a syntax error.

❓ state_output

advanced

What is the output when accessing /api/items?

Consider this NestJS controller. What will be the response body when a GET request is made to '/api/items'?

NestJS

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

@Controller('api/items')
export class ItemsController {
  @Get()
  getItems() {
    return { count: 3, items: ['a', 'b', 'c'] };
  }
}

A ["a","b","c"]

B {"count":3,"items":["a","b","c"]}

C 3

D Error: Route not found

💡 Hint

The method returns an object literal which NestJS serializes to JSON.

The getItems() method returns an object with count and items. NestJS automatically converts this to JSON in the HTTP response.

🔧 Debug

advanced

Why does this controller method never get called?

Given this controller, why does the method not respond to any HTTP requests?

NestJS

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

@Controller('tasks')
export class TasksController {
  getTasks() {
    return 'Task list';
  }
}

A The controller class is missing the @Injectable() decorator.

B The controller path 'tasks' is invalid and blocks all routes.

C The method name getTasks is reserved and ignored by NestJS.

D The method is missing the @Get() decorator, so it is not registered as a route handler.

💡 Hint

Check if the method has the correct HTTP method decorator.

In NestJS, methods must have decorators like @Get() to handle HTTP requests. Without it, the method is not exposed as a route.

🧠 Conceptual

expert

What is the effect of multiple @Controller decorators on one class?

In NestJS, what happens if a class is decorated with multiple @Controller decorators like this?

  @Controller('beta')
  @Controller('alpha')
  export class MultiController {
    @Get()
    getData() {
      return 'data';
    }
  }

A Only the last @Controller decorator ('beta') is applied, so the base path is '/beta'.

B The class will handle routes for both '/alpha' and '/beta' base paths.

C NestJS throws a runtime error due to multiple @Controller decorators.

D The class is ignored and no routes are registered.

💡 Hint

Consider how decorators are applied in TypeScript and NestJS.

In TypeScript, decorators are applied bottom-up. The last @Controller decorator overwrites the previous one. So only '/beta' is used as the base path.