Encapsulated Class Hierarchy with Private Field Interceptors in Service Classes

export class BaseServiceHandler {
  #secretKey;
  constructor(secretKey) {
    this.#secretKey = secretKey;
  }
  get secret() {
    return this.#secretKey;
  }
  execute(req) {
    throw new Error("Abstract method execute() must be overridden");
  }
}
 
export class UserRegistrationHandler extends BaseServiceHandler {
  #allowedRoles = new Set(['admin', 'editor', 'viewer']);
  execute(payload) {
    if (!this.#allowedRoles.has(payload.role)) {
      return { success: false, reason: "Invalid role delegation" };
    }
    return { success: true, digest: `${payload.username}:${this.secret}` };
  }
}