fig-1.js

class CustomError extends Error {
  constructor(statusCode, { key, message }) {
    super(message);
    this.statusCode = statusCode;
    this.key = key;
  }
}

export class BadRequestError extends CustomError {
  constructor({
    key = 'BAD_REQUEST',
    message = 'Bad Request',
  } = {}) {
    super(400, { key, message });
  }
}

class InternalServerError extends CustomError {
  constructor({
    key = 'INTERNAL_SERVER_ERROR',
    message = 'Internal Server Error',
  } = {}) {
    super(500, { key, message });
  }
}

const error = new Error();
error instanceof CustomError; // false

const internalServerError = new InternalServerError();
internalServerError instanceof CustomError; // true
internalServerError.statusCode; // 500
internalServerError.key; // INTERNAL_SERVER_ERROR
internalServerError.message; // Internal Server Error