How to create and use custom decorators in NestJS?

Custom Decorators in NestJS

NestJS extensively uses TypeScript decorators for metadata-driven development. You can create your own decorators to reduce boilerplate and add reusable behavior.

Types of Custom Decorators

1. Parameter Decorator

Extract data from the request:

typescript

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export const CurrentUser = createParamDecorator(
  (data: string, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    const user = request.user;
    return data ? user?.[data] : user;
  },
);

Usage:

typescript

@Controller('profile')
export class ProfileController {
  @Get()
  getProfile(@CurrentUser() user: User) {
    return user;
  }

  @Get('email')
  getEmail(@CurrentUser('email') email: string) {
    return { email };
  }
}

2. Metadata Decorator with SetMetadata

typescript

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

export const Roles = (...roles: string[]) => SetMetadata('roles', roles);
export const Public = () => SetMetadata('isPublic', true);

Used with Guards:

typescript

@Controller('admin')
export class AdminController {
  @Get('dashboard')
  @Roles('admin', 'superadmin')
  getDashboard() {
    return { message: 'Admin dashboard' };
  }

  @Get('health')
  @Public()
  healthCheck() {
    return { status: 'ok' };
  }
}

3. Composed Decorator

Combine multiple decorators into one:

typescript

import { applyDecorators, UseGuards, SetMetadata } from '@nestjs/common';
import { ApiBearerAuth, ApiUnauthorizedResponse } from '@nestjs/swagger';

export function Auth(...roles: string[]) {
  return applyDecorators(
    SetMetadata('roles', roles),
    UseGuards(JwtAuthGuard, RolesGuard),
    ApiBearerAuth(),
    ApiUnauthorizedResponse({ description: 'Unauthorized' }),
  );
}

Usage — clean and DRY:

typescript

@Controller('users')
export class UsersController {
  @Get()
  @Auth('admin')
  findAll() {
    return this.usersService.findAll();
  }
}

4. Class Decorator

typescript

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

export function ApiController(prefix: string) {
  return applyDecorators(
    Controller(`api/v1/${prefix}`),
    UseInterceptors(LoggingInterceptor),
    UseInterceptors(TransformInterceptor),
  );
}

typescript

@ApiController('users')
export class UsersController {
  // All routes prefixed with /api/v1/users
  // LoggingInterceptor and TransformInterceptor applied
}

5. Property Decorator (for Validation)

typescript

import { registerDecorator, ValidationOptions } from 'class-validator';

export function IsStrongPassword(validationOptions?: ValidationOptions) {
  return function (object: object, propertyName: string) {
    registerDecorator({
      name: 'isStrongPassword',
      target: object.constructor,
      propertyName,
      options: validationOptions,
      validator: {
        validate(value: string) {
          return /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&]).{8,}$/.test(value);
        },
        defaultMessage() {
          return 'Password must contain uppercase, lowercase, number, and special character';
        },
      },
    });
  };
}

Summary

Decorator Type	Use Case	API
Parameter	Extract request data	`createParamDecorator()`
Metadata	Set metadata for Guards/Interceptors	`SetMetadata()`
Composed	Combine multiple decorators	`applyDecorators()`
Class	Apply to entire controller/class	`applyDecorators()`
Property	Custom validation rules	`registerDecorator()`

Best practice: Custom decorators are powerful for reducing boilerplate. Create @Auth(), @CurrentUser(), and @Public() decorators in every NestJS project — they're used constantly.

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