Reflector and custom decorators in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a custom decorator that sets metadata with the key 'role'.

NestJS

import { SetMetadata } from '@nestjs/common';

export const Roles = (role: string) => SetMetadata('[1]', role);

Drag options to blanks, or click blank then click option'

Arole

Baccess

Cpermission

Droles

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular 'role' instead of 'roles' causes metadata retrieval issues.

Using unrelated keys like 'permission' or 'access' won't match expected metadata.

The metadata key used in NestJS examples for roles is usually 'roles'. This key is used later to retrieve the metadata.

2fill in blank

medium

Complete the code to inject Reflector in a guard constructor.

NestJS

import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
import { Reflector } from '@nestjs/core';

@Injectable()
export class RolesGuard implements CanActivate {
  constructor(private readonly [1]: Reflector) {}

  canActivate(context: ExecutionContext): boolean {
    // guard logic
    return true;
  }
}

Drag options to blanks, or click blank then click option'

AReflector

Breflector

Creflect

DreflectorService

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'Reflector' as variable name causes errors.

Using unrelated names like 'reflect' or 'reflectorService' breaks convention.

The injected Reflector instance is usually named 'reflector' in the constructor for clarity and convention.

3fill in blank

hard

Fix the error in retrieving metadata inside the guard using Reflector.

NestJS

const roles = this.reflector.get<string[]>('[1]', context.getHandler());

Drag options to blanks, or click blank then click option'

Aroles

Brole

Cpermission

Daccess

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular 'role' causes the metadata to be undefined.

Using unrelated keys like 'permission' or 'access' returns no metadata.

The metadata key must match the one used in the custom decorator, which is 'roles'.

4fill in blank

hard

Fill both blanks to create a custom decorator and retrieve metadata in a guard.

NestJS

export const Roles = (role: string) => SetMetadata([1], role);

const roles = this.reflector.get<string[]>([2], context.getHandler());

Drag options to blanks, or click blank then click option'

A'roles'

B'role'

C'permissions'

D'access'

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys in decorator and reflector causes metadata mismatch.

Forgetting quotes around the key causes syntax errors.

Both the decorator and the reflector must use the same metadata key 'roles' to work correctly.

5fill in blank

hard

Fill all three blanks to create a guard that checks roles metadata and returns access decision.

NestJS

canActivate(context: ExecutionContext): boolean {
  const roles = this.reflector.get<string[]>([1], context.getHandler());
  if (!roles) {
    return [2];
  }
  const request = context.switchToHttp().getRequest();
  const user = request.user;
  return roles.some(role => user.roles?.includes([3]));
}

Drag options to blanks, or click blank then click option'

A'roles'

Btrue

Crole

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Returning false when no roles metadata causes unwanted blocking.

Using wrong variable names inside the some() callback causes errors.

Using wrong metadata key causes roles to be undefined.

The guard retrieves 'roles' metadata, returns true if no roles are set, and checks if the user has any required role.