Object-Oriented Command Stack Encapsulation using JS Private Fields and Proxies

class Command {
  execute() { throw new Error('Abstract method'); }
  undo() { throw new Error('Abstract method'); }
}
 
export class TransactionManager {
  #undoStack = [];
  #redoStack = [];
 
  execute(command) {
    if (!(command instanceof Command)) throw new TypeError('Invalid command instance');
    command.execute();
    this.#undoStack.push(command);
    this.#redoStack.length = 0;
  }
 
  undo() {
    const cmd = this.#undoStack.pop();
    if (cmd) {
      cmd.undo();
      this.#redoStack.push(cmd);
    }
  }
}