Custom TypeScript decorator for plain objects

dto.ts

import { IsString, IsOptional } from 'class-validator';
import IsPlainObject from '../isPlainObject.decorator';

export class Dto {
  @IsOptional()
  @IsPlainObject()
  readonly data?: object;
}

IsPlainObject.decorator.ts

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

@ValidatorConstraint({ async: true })
export class ValidateObject implements ValidatorConstraintInterface {
  validate(data: object, args: ValidationArguments) {
      return data.constructor === Object;
   }
}

export default function IsPlainObject(validationOptions?: ValidationOptions) {
  return (object: object, propertyName: string) => {
    registerDecorator({
      target: object.constructor,
      propertyName,
      options: validationOptions,
      constraints: [],
      validator: ValidateObject,
    });
  };
}